strange behavior of my player in the game

I was winning 2:0 during the match (final Champions league). After the end of the bonus of 15% attacking I switched the bonus to 15% defence during the game. After the switch of the bonus from attacking to defence my player MR (6 stars) fouled the opponent player from behind immediately. Of course I got a red card and I Iost the match 3:2. Why did my player do that when my team was leading 2:0? Strange...

my setup of tactics was during the game:
team mentality: Normal
Force counter att.: off
pressing style: low
Tackling style: normal
marking style: zonal