Kinematic Analysis of the Slap Hitting Technique in Division I Softball Players

Submitted by Robin Lund1, Ph.D.*, Travis Ficklin2, Ph.D.* Mr. Johnathan Faga3*, Ms. Cassie Reilly-Boccia4*

1* Assistant Professor of Physical Education at University of Northern Iowa, Cedar Falls, IA 50614

2* Assistant Professor of Physical Education at University of Northern Iowa, Cedar Falls, IA 50614

3* B.A. in Movement and Exercise Science from the University of Northern Iowa.

4* Director of Research and Development at Athletes Warehouse in Pleasantville, NY.

ABSTRACT

The purpose of this study was to provide a kinematic description of the phase parameters of the slap hitting technique and the interrelationships that may exist in Division I softball players.  Video data were collected for all swings during a 15-game softball tournament in which six NCAA Division I teams played.  A high-speed video camera filming at 300 Hz was located along the third base line recording every pitch.  Only data from trials in which a slap swing attempt was made were kept, resulting in 200 trials.  Three phases were identified; preparatory step, wind-up and swing.  The duration of each phase (tPREP, tWIND-UP and tSWING, s) as well as the duration of the entire technique (tTOTAL, s), the forward velocity of the hips (vHIP, m/s) during the wind-up phase and the velocity of the bat at contact (vBAT, m/s) were obtained for each trial.  Descriptive statistics were calculated for each of the variables and Pearson product moment correlations were used to examine the relationships among the variables.  Several significant relationships were identified (p<0.05).  The duration of the preparatory step phase has a direct effect on vHIP and vBAT.  The duration of the wind-up and swing phases appear to be related to the timing of each individual trial and do not appear to play a role in vHIP and vBAT.  Coaches should consider the role of the preparatory step phase on vHIP and vBAT when coaching different techniques such as the soft slap and the power slap.

Key words: softball, kinematic, slap hitting.

INTRODUCTION

One of the major distinctions between the sports of baseball and softball is the slap-hitting technique.  Mainly used by players possessing above average running speed, this technique involves hitting the ball while running forward from the left-hand batters box (2).  Qualitative analysis of 200 slap technique video clips performed by 20 different players, resulted in the identification of the preparatory step, wind-up and swing phases.

The preparatory step phase is initiated when the lead foot leaves the ground (Figure 1) and begins moving backwards towards the rear foot.  This phase ends when the lead foot makes contact with the ground and the rear foot leaves the ground, which begins the wind-up phase (Figure 2).  This phase is characterized by pushing off with the rear leg and stepping over and in front of the lead foot in a running motion.  The upper body maintains position while the player moves forward.  This phase ends when the rear foot reestablishes contact with ground and marks the beginning of the swing phase (Figure 3).  In this phase, the bat is swing forward much like a traditional swing while the legs continue to move in a running motion.  The swing phase ends when the bat makes contact with the pitch (Figure 4).

The time in which this technique became mainstream is unclear but slapping has gained popularity and has become an important aspect of offensive strategy for most teams.  Although many coaches recommend that this technique should be taught to players who are fast but weaker offensively (1), the offensive potential of this technique should not be underestimated.  Analysis of the National Collegiate Athletic Association statistics for the 2012-13 season indicate that of the players with the ten highest batting averages, six used the slap technique (6).

There are many reasons to account for the effectiveness of the slap hitting technique.  Slap hitters do not swing as hard as possible.  Players using this technique may experience greater bat control and may strike out less than players using a traditional swing.  Additionally, the ability to hit the pitched ball to a desired location regardless of pitch location allows the slap hitter to potentially take advantage of different defensive alignments.  Conversely, players using a traditional swing are only concerned with the exit velocity of the batted ball.  Finally, making contact while running reduces the time needed for the batter to reach first base.  The result is that a ball struck with the slap hitting technique puts greater pressure on the defense to field the ground ball cleanly due to these time constraints.

Interestingly, despite the rise in popularity and the effectiveness of this technique, very little research has been performed in this area.  The purpose of this study was to define and provide a kinematic description of the phase parameters of the slap hitting technique and interrelationships that may exist in Division I softball players.

METHODS

Subjects

These data were collected during sixteen Division I softball games that occurred at a tournament during the 2012-13 season.  From the six teams taking part in the tournament, twenty players were identified who used the slap hitting technique.  The Ratings Percentage Index (RPI) for the teams at the time of competition ranged from 1 to 271.  Participants were between the ages of 18 and 23 years old.  The twenty hitters attempted 200 slap swings, which were analyzed for this study.  All procedures were reviewed and were considered exempt by the Internal Review Board at the University of Northern Iowa.

Instrumentation

High-speed video data (300 Hz) were collected for all slap attempts during the games (JVC GC-PX1, Tokyo, JP).  The videos of the slaps were converted to AVI format and transferred to the Maxtraq (Innovision Systems, Inc., Columbiaville, MI) software for digitizing.  Digitized data were exported in comma separated value files and analyzed using custom Matlab software (Mathworks, Natick, Massachusetts) to carry out computations for each trial.

Procedures

A camera was positioned on the third-base side of the field with the optical axis even with and parallel to the front edge of home plate.  This camera was used to capture any slaps made by left-handed hitters.

The resulting video clips were trimmed and converted to the AVI format for use in the MaxTraq digitizing software.  For distance calibration, reference points at the apex of home plate, at the inside front corners of the batters boxes, and the three remaining corners of the lefthanded batters box were digitized (7).  All games were played on an artificial surface, therefore the batters boxes remained intact throughout the tournament, making these points reliable from game to game.

For temporal measurements, the onset of the preparatory phase was identified as the video frame in which the right (lead) foot of the batter left the ground to begin the motion.  The frame in which the left foot then left the ground was identified as ending the preparatory phase and was the onset of the wind-up phase.  Next, the frame in which the left foot touched down again was deemed to be the end of the wind-up phase and the start of the swing phase.  This last phase ended at impact, which was the frame in which the ball was either contacted or, in the event of a miss, the frame in which the horizontal position of the ball reached that of the bat.

The locations of the hips were digitized at the onset and termination of the wind-up phase.  Additionally, the position of the bat end was digitized at impact and then four frames prior (4,7).

A distance calibration was made for converting digitized pixel units to real-life meters.  For bat velocity calculations, a calibration was made by establishing a scale factor of meters-per-pixel in the horizontal direction.  First the location of the centroid of the two inside corners of the batters boxes was calculated from the digitized data.  Then the known distance between this centroid and the apex of home plate (1.4351 m) was divided by the same distance as measured in pixels.

To later calculate the velocity of the hips, similar centroids were calculated for the front center and rear center of the lefthanded batters box based upon the locations of all four corners.  Then, the known length of the batters box (2.1336 m) was divided by the distance between these new centroids, which is the length of the batters box in pixels when measured through the middle of the box.

Locations in meters were computed for the bat end and a mid-hip point in the applicable frames and using the appropriate scale factors.  All time durations were found by multiplying the number of video frames in the period by 1/300 s (5).  Accordingly, tPREP, tWIND-UP, and tSWING were computed, as well as the 1/75th s time period spanning the period between impact and four frames prior.  Hip velocity (vHIP) was calculated by dividing the horizontal change in mid-hip position during the wind-up phase by the phase duration in seconds.  Bat velocity (vBAT) was derived by dividing the bat end change in position during the last four frames leading to impact by 1/75 s (7).  These data collection methods and calculations have been demonstrated to be valid and reliable (4).

Statistical Analysis

The duration of the total technique and each individual phase (tTOTAL, tPREP, tWIND-UP and tSWING, s) were obtained for each swing.  Additionally, the forward velocity of the hips (vHIP, m/s) during the wind-up phase and the velocity of the bat at contact (vBAT, m/s) were calculated.  Descriptive statistics (mean ± SD) were calculated for all variables.  Pearson product moment correlations were used to examine the relationships among the variables.  Alpha was set at p<0.05 for all inferential statistical analyses.

RESULTS

All descriptive statistics for each of the variables can be found in Table 1.  Pearson product moment correlations can be found in Table 2.

DISCUSSION

The purpose of this study was to define and provide a kinematic description of the phase parameters of the slap hitting technique and interrelationships that may exist in Division I softball players.  To the knowledge of the authors, this is the first study to report and analyze the slap technique in softball.  Each of the kinematic variables demonstrated a wide range of values indicating that players used different strategies to perform this technique.  For example, the soft slap and power slap techniques are used specifically to bat the ball on the ground with either low or high exit velocities depending on the game situation.  Despite this variability, clear patterns emerged upon qualitative analysis of the video clips.

The slap technique is initiated by moving the lead foot backwards towards the rear foot.  This event defines the beginning of the preparatory step phase.  This phase ends when the lead foot reestablishes contact with the ground.  The preparatory step phase is important because the feet become positioned behind the center of mass allowing the athlete to create a horizontal impulse resulting in forward acceleration(3).  The duration of this phase varied greatly and ranged between 0.06-0.40 s.  Significant correlations (p<0.05) were observed between tPREP and several other variables indicating the importance of this initial movement.  A longer preparatory step time was significantly correlated with a greater tWIND-UP (r=0.31), vHIP during the wind-up phase (r=0.44) and vBAT (r=0.35).  These results suggest that a longer preparatory step moves the feet behind the center of mass.  This will increase the ability to generate horizontal impulse and subsequent acceleration forward through the batters box during the wind-up phase.  This ultimately results in greater vHIP and vBAT.

Although, tWIND-UP had a moderately strong relationship with vHIP (r=0.38), there was virtually no relationship with vBAT (v=0.07).  Weak relationships between tSWING and vHIP (r=-0.12) and vBAT (r=0.08) were also observed.  The duration of these phases may be dependent on the timing of the movement rather than the kinematic outcome of the hips and bat.  For example, if the process starts too soon, the swing phase is lengthened in relation to the wind-up phase because the swing must be delayed while waiting for the pitch.  The opposite would be true if the process was started too late.  With recognition that the process has started late, the swing is initiated sooner relative to the wind-up phase which reduces the time between rear foot ground strike and ball contact with the bat resulting in a short swing phase.  The moderately strong negative relationship between tWIND-UP and tSWING support this contention (r=-0.53).  The strong relationship between tPREP and tTOTAL (r=0.90) is more evidence to support the importance of the preparatory phase in regards to the kinematic outcomes.  The relationship with tTOTAL were much weaker with tWIND-UP (r=0.49) and tSWING (r=0.17) which further strengthens the notion that duration of these two phases are indicative of variations in timing as opposed to directly affecting vHIP and vBAT.

A large amount of variation was observed in vHIP and vBAT.  An interesting characteristic of the slapping technique is that the quality of contact or the exit velocity of the batted ball will most likely not correlate with statistical performance.  A perfectly timed slap resulting in a batted ball with high exit velocity has the same chance of getting past the infielders as a ball batted with a traditional swing.  However, a batted ball with poor exit velocity as a result of poor quality of contact is often very effective in slapping due to the reduced time taken to run to first base compared to a traditional hitter.  For this reason, value should not be placed on vBAT alone.  Rather, coaches and players should recognize that different situations might call for different tactics (i.e. power slap vs. soft slap), which can be affected directly by variations in the preparatory step phase of the technique. The authors of this study also recognize that increasing the length of the preparatory phase will also increase the total time to perform the technique.  Under these circumstances, the preparatory step would need to be initiated earlier relative to the pitched ball, which could have negative implications regarding timing the pitch in a game situation.

CONCLUSIONS

In conclusion, this study identified three phases that occur during the slap hitting technique.  The variables vHIP and vBAT will not necessarily affect statistical performance.  However, the preparatory step phase may have a direct effect on vHIP and vBAT and that coaches should consider this phase when training the use of a hard or soft slaps during game play. The effects of manipulating the preparatory phase on timing should also be considered. Future work should attempt to determine the effects of specific slap kinematic parameters on actual statistical outcomes associated with game play.

APPLICATIONS IN SPORT        

Most coaches agree that all players who use the slap technique should strive to become a “triple threat.”  In the softball world, this describes those who able to bunt, soft slap and power slap.  Coaches should discuss the importance of the preparatory step and develop drills that focus on manipulation of the preparatory step to achieve changes in hip and bat velocity.

ACKNOWLEDGEMENTS           

We would like to thank Kayla Braud, Emily Allard and Kristen Jensen for their feedback during the writing process.  We also would like to thank Kayla Braud for allowing us to use her likeness in the manuscript.

REFERENCES

  1. American Sport Education Program. (2009). Coaching softball: Technical and tactical skills. Champaign, IL: Human Kinetics.
  2. Chang, Y., Hsieh, H., Yang, S., Chen, F., Lin, H., & Wu, H. (2011). Comparison of torso twist between slap hit and ordinary hit in softball batting. Portugese Journal of Sport Sciences, 11, 61-63.
  3. Cusick, J., Lund, R. & Ficklin, T. (2014). A comparison of three different start techniques on sprint speed in collegiate linebackers. Journal of Strength and Conditioning Research, 28(9), 2669-2672.
  4. Ficklin, T., & Lund, R. (2014). Validation of a two-dimensional video method for measuring in-game softball bat velocity. Paper presented at the World Congress on Biomechanics, W469.
  5. Ficklin, T., Lund, R., & Schipper, M. (2014). A comparison of jump height, takeoff velocities, and blocking coverage in the swing and traditional volleyball blocking techniques. Journal of Sports Science and Medicine, 13, 73-78.
  6. National Collegiate Athletic Association. (n.d.). Batting average. Retrieved from http://www.ncaa.com/stats/softball/d1/current/individual/271.
  7. Reilly-Boccia, C., Ficklin, T., Lund, R., Hervas, J., & Beatty, K. (2013). Bat quickness and bat velocity in Division I softball players. Paper presented at the 37th Annual Meeting of the American Society of Biomechanics. Abstract retrieved from http://www.asbweb.org/conferences/2013/abstracts/447.pdf

Table 1

Table 2

Figure 1

Figure 1. Beginning of the preparatory step phase.

Figure 2

Figure 2. End of the preparatory step phase and beginning of the wind-up phase.

Figure 3

Figure 3. End of the wind-up phase and beginning of the swing phase.

Figure 4

Figure 4. End of the swing phase.

 

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