How can you block if you don't have the ball? I've seen defenders take out blockers like this all the time. You're not supposed to go low on an engaged player when you're blocking on OFFENSE - I get that. Is this an obscure rule I don't know? Never seen it called that I'm aware of... and twice today. Brutal.
Blocking on defense has rules as well. 100% right call in both situations. Defense has to be trying to make tackle to go low. No one can go low on punt or kickoff.