Bingo! Most fans don't understand it. It took me 5-6 years of officiating before I really understood it and had it simplified for me. Here is a quick primer for the Bison fans!
For OH it should fall into one of these 6 categories:
1) Grab and restrict - grab someone who has beat you and take away a step at the point of attack
2) Hook and restrict - hook someone usually high and bend them backward
3) Jerk and restrict - usually a jersey tug that takes you away from the point of attack just brief enough to not make a play
4) Take down - usually the result of a blocker getting in the chest of a defender and twisting him down to the ground
5) Tackle - usually grabbing a defender around the legs/ankles and tackling him
6) Pull over - lineman grabs defender and falls backward pulling defender on top of him - hard to distinguish from a successful bull rush by the defender
In most cases offensive holding happens when the blocker is beat (i.e. no longer between the defender and the runner). We use the phrase "feet beat cheat." A good block can quickly turn into a hold depending on which side of the blocker the defender goes. For example, a TE is facing the sideline and has the defender sealed off for an inside run. But the runner chooses to go outside instead. If the defender tries to turn to pursue that runner and blocker prevents him that is likely holding.
Holding often occurs on the edges by pulling linemen or receivers. Receivers downfield also can get into trouble. Check out the block by #19 on the 3rd down TD scramble by Lance. When he initially makes contact at the 25 he gets the defender into a backpedal. At that point the defender is beat and it is very unlikely that will turn into a hold. But if the defender is able to get leverage and try to shed the block (which he does around the 15) it can turn into a hold if the blocker doesn't let go. I often tell blockers the release is important once the defender is in position to move away from you. I thought his actions on this play could have been a hold and would probably be supported. I showed it to several other college officials (most of whom watched the game!) and it was split 50/50. Those who wouldn't have called it said by the time he tries to turn and the restriction happens the runner was already gone. Others said it was still a big restriction out in the middle of everyone to see. The officials on this play probably went with the former.
Other key terms to actually have a holding foul are "material restriction at the point of attack." If it happens on a short dive up the middle or as part of a double team (unless he breaks away from one of them and the other is restricting him) we usually let that go. If the defender commits late one direction or the other let it go. He beat himself. If you see a jersey tug make sure it actually took a step away from the defender. Sometimes it doesn't even slow them down (parents with small kids can relate).
Here is a flyer produced by Referee Magazine several years ago that discusses the categories as well. These aren't listed in the rule book, but they are commonly used when teaching officials how to call holding CONSISTENTLY. If you are a coach and you get called for holding, ask the official which category it was in. If he can answer you probably have a decent official.
https://kvfoa.org/clinician/kvfoa.or...of%20Holds.pdf