## 4 Discussion  
This is the first study to examine the impact of the format change from two halves to four quarters, along with the rule change of stopping the clock for penalty corners in collegiate women's field hockey athletes. Therefore, this also is the first study to report activity profiles of Division I college athletes with the current timing system. While an increase in the number of substitutions as well as a decrease in match time was noted, overall, the change in format had minimal impact on player performance profiles and specifically on player's TD, LSR, HSR, MV, and relative measures. One notable implication resulting from this overall minimal impact is that this study demonstrates most work related to player training and performance remains valid despite the rule changes. Also, while the games were shorter in the new format, the lack of player activity change implies coaches are able to play their top athletes to a similar degree while not degrading their overall performance while lessening the amount of time the subbed athletes might play. A prior study examined the same format change in elite female athletes at the international level [18]. A similar significant decrease in match time was observed. To allow a direct comparison of activity levels per time on the field before and after the rule change and to compare to international play, the time on the field used for 2019 included the duration of penalty corners. In international competition, the clock is stopped for 40 s for penalty corners, whereas, after the format change in Division I college field hockey, the referees control the restart of the game with the insertion of the penalty corners. The average penalty corner time in 2019 reported in this study (41.4 \(\pm\) 8.3 s) is comparable to the 40 s required stoppage time in international play. The match time difference across years in this study is approximately 5 min shorter in 2019 compared with 2018, which is a result of a 10 min shorter game, but 6 more minutes for average penalty corner stoppage, and 1 min less on average with no time outs, with all other referee and goal stoppages of the clock being approximately equal. As seen from the standard deviation for match time in 2019 being twice that of 2018, the variability is because the number of penalty corners fluctuates. Considering the results changing across years, both overall and for specific positions, comparisons can be made to a similar study, which also noted a higher number of substitutions after the rule change in elite athletes, both in an absolute and relative sense [18]. This increase in substitutions in both studies could be a result of substitutions that occur during breaks between periods. After the rule change, there were four periods with three breaks rather than two periods with one break. This allowed for more natural opportunities to perform substitutions outside the active run of play. Substitutions during breaks are easier to perform for athletes primarily playing on the opposite side of the field from the bench or in key positions related to defending the goal. Performing a substitution during active play requires a player in a key location to be absent for a period of time. Substituting during breaks eliminates this concern. Such a substitution during play at the elite level may be easier to perform than at the collegiate level, thus explaining the increase in substitutions for defenders in this study. This variation in substitutions approach across format change for defenders relative to those of elite athletes also helps to explain the increased HSR for defenders in this work after the rule change. The rule change did not have a noted impact on substitutions for forwards or midfielders. While this study showed a change in relative HSR for forwards before and after the rule change, a similar difference was not seen in prior research at the elite level [18]. One difference between the two studies is the prior study did not include player data if they fell below a set threshold in playing minutes.