Football is a tough game.
When you have the benefit of instant replay, it looks like guys on the field actually make decisions about where and how they hit other players.
In actual game time, these "decisions" are rarely made. Things happen fast on the field. The smallest little decisions on angles of pursuit and physical positioning of the body during a play determine the end result of a play, and these things are frequently instinctive rather than conscious choices.
I'd wager that you would have a hard time finding a coach who actually teaches techniques to hurt other players. Injuries like this are bad luck more than anything else. When a player lines up across form another player, even with the notion of hurting him, all sorts of things have to line up perfectly for that player to get his wish.
This really sucks for Irby and for the Longhorns. This injury makes reminisce about Scaife, and it might have the same impact over time. It really sucks.