Instruction must have changed since I played, although I never played college ball. My coaches instructed to tackle either:
- go chest high, wrapped up upper body, facemask up (see what I'm hitting), drive through or
- go waist low, wrapped up thighs, facemask up (drilled that into us), drive through, pull the ball carrier down, using both your weight and strength. Never slide the hold pass the knees.
Perhaps we always had enough players who could execute tackling that way because players too light and could not execute did not see the field often until they could. That was late 70's and early 80's for me.
Nowadays, it is really common seeing tacklers sliding the hold down the legs or just straight out going for the runner's ankles. Not sure what my coaches would have said about the former but they always said going too low for a tackle would likely result in a missed tackle.