Forced subs maybe? All the players wear heart rate monitors these days. Their work rate is being tracked live by the coaching staff. The coaches will know how many meters they’ve covered, tackles made, heart beats per minute etc. More importantly the coaches can see when their HR does not return to recovery levels as it should, HR is getting laboured – meaning the player is getting tired. If a tired player misses a tackle it is not his fault. It’s the fault of the coaches who didn’t take him off in time. I would guess with the intensity of a hiveld test some of the player ‘had to be taken out’.