defensive holding

[Jim D]

This is definitely a foul but you have to see it in context to decide whether to call it or not. As the others mentioned, if the idea of holding a tackle is to let a defensive linebacker charge through the line, then it has to be called for sure. If the tackle is going after the end, then there is not impact so you let it go. If the offensive tackle is not going after the and is taking off after someone else, then I would call it as B's holding is disrupting Team A's blocking scheme.

I had a high school game as Umpire once and the offensive center and defensive nose guard held each other on every play. When possession switched, the center became the nose guard and vice versa and they continued to dance with each other. it made my job very easy as I had too less players to watch.