One thing about playing sport, is that one has to become used to pushing through the physical discomfort of pushing themselves past their perceived limits.
It is not so noticeable in adult sport, as those who have been playing for long enough have learnt to push themselves through that discomfort that they feel, and by pushing themselves through that discomfort, they’ve expanded out what they’ve become capable of.
Some kids naturally push themselves through that discomfort, but others get to that point and you can see them back away, thereby their effort on the field drops away.
And as most who are coaching know and realise, if one is not pushing themselves on the field, one is not in the game.
So one may have 11 players on the field, but if 6 aren’t pushing themselves through that discomfort, realistically, you’ve only got 5 players actively engaged in the game.
So the act of actively pushing oneself through that physical discomfort is one of the break through marks for truly becoming involved into the game.
Become comfortable with the discomfort to extend ones’ game