This makes sense. If you want to train football....then play football. Sprints, balance, calisthenics etc are all fine, but the functional training is in the game
Heart Rate Responses During Small-Sided Games and Short Intermittent Running Training in Elite Soccer Players: A Comparative Study.
The purpose of this study was to compare heart rate (HR) responses within and between physical controlled (short-duration intermittent running) and physical integrated (sided games) training methods in elite soccer players.
In conclusion, these findings showed that some small-sided games allow the HR to increase to the same level as that in short-duration intermittent running. The sided game method can be used to bring more variety during training, mixing physical, technical, and tactical training approaching the intensity of short-duration intermittent running but with higher intersubject variability.