Everything. He's a willing guy but look at how he came up and tried to make that play. Look at his form. If I were trying to make video on "how not to do this", that would be it.
First of all, you don't lead with your head, you use your shoulder. You don't go head up on a guy that has 40 or 50 pounds on you, that's stupid. You get lower then the other guy and if you are 5'10/5'11, that shouldn't be that hard to do. Use your shoulder, get into his legs and use and angle. Going head up with your head down and going in high is asking to get hurt. I don't pay you to be on the IR. I pay you to be on the field, making plays. Of course you don't expect this guy to stop Zeke by himself on the goal but that's not how you teach the game. Get into him, slow him down, wait for help. Do those things and you've done your job. If other guys don't get there to give help, that's on them but your job is simple in that situation. Kazee did none of those things there and what's more, he got himself hurt and that hurt the team. You gotta be smarter then that.