I vividly remember a former coach of mine reprimanding me for slipping on a hard cut at the line of scrimmage, "killing" the play where my body fell. I also remember being reprimanded again (for the same play) the next day watching the film of the scrimmage. I thought, 'it's not like I was trying to slip'.
Fast forward to today. Having put quite a few athletes through change of direction tasks, I think twice about reprimanding an athlete for slipping on a change of direction move - especially if it was one made out of aggressiveness.
Often, I don't say anything. Other times, I commend it. I don't coach an athlete loose their footing, but I do compliment them if it was caused by aggressiveness. Coaching is as much as what you don't say, as you do. Sometimes great abilities come with potential costs... costs that just need to be managed as best as possible.
The mechanics of effective change of direction requires instability - getting the center of mass to fall outside the body (to either push or resist it's velocity). With greater velocities, this means teetering the 'edge' of losing friction. The most agile athletes (in terms of changes in velocities) are those that are comfortable getting into these unstable positions; positions where there is no other option than using intense force production/reduction and rates to keep them from falling. And sometimes athletes are bold enough in their bodies that they will create such extreme forces and angles, that friction will be missed.
I've seen it happen to Adrian Peterson quite a few times, which is likely part of the reason he is the player he is. By mentioning him in this post along with myself, puts us in the same category, right?.
The "pro agility" drill, while artificial, is a test I like to use both quantitatively and qualitatively. Qualitatively, I assess athletes ability and comfort level of getting in and out of these acute angles (or lack thereof). For conditioning, multiple power, jump cuts and stops, and putting them to application in different tag and mirror games, are some ways of trying get the point across. The big message I tell them is to 'assaulting the ground', as opposed to 'tiptoeing through flower gardens'. Sometimes descriptive language helps too; "catch the ground", "on a dime", "vicious angles", etc.
Interestingly, I see the 'tiptoeing' more from the athletes that have specialized in one sport for much of their organized sporting careers as opposed to multiple. (It's funny that I call them 'athletes', when they are specialists)
Just as many of the tactical aspects of games are about angles, so are the technical in creating the appropriate angles for powerful movement - angles and Newton's laws
Don't squander aggressiveness, encourage an athlete to harness it.