There are an awful lot of potential tactical and personnel factors. For example, does your tactic leave him exposed and so he's having to make riskier challenges to try and stop attacks? Alternatively, are the nearest players to him in midfield and the player ahead of him on the pitch not the best/most hardworking defensively and so he's ending up compromised in that manner.
You can use ease off tackles on defenders. Realistically to look into this we'd need to see what your tactical set-up is like, and pkm's of where you feel the player making the wrong challenge that results in a booking occur. Should you have any pkm's you wish to share, a guide on how to do so is available here: