It is legal to grab the back of the pads. You can not pull the player down through the tackle, backwards to the ground. He was close to going forward which is why it wasn't called. It is one of the least understood penalties in fb.
If you think any umpire wants anything to do with a te running the middle you should have your brain examined. Teams use the umpire to get seperation from a defender. In this instance he got too close. \
This crew called a ton of penalties against MSU, lots of holds that hurt them, not one hold on us, and the ref showed GREAT restraint by making a possible unsport. conduct a warning. They missed a dpi in the 1st half, but overall they were fine imho.