Foul on Dalton Nixon's breakaway was kind of thing that starts fights
I'm not sure if it was dirty or not, but it was extremely ill-advised. Guys coming from behind had very little chance of making a block without committing a very hard foul, knowing that Nixon is going to be in the air, very vulnerable and unable to defend himself from behind.
So, it's a play as a defender you know you have very little chance making a clean block, but are likely to injure a guy on.
Pretty crappy thing to do