A player that largely stays in our forward half of the ground who primary task is to lock the ball in there. Chase, tackle or force a turnover (in other words). Nyhuis was given the task of shutting down Chris Tarrant's younger brother - instead of providing leads or presenting himself as a target for the ball coming in, he was meant to run with Robbie and limit his effectiveness down there. This is a sharp deviation from Chris Mayne's role - which was similar, but more about forcing a turnover and/or presenting himself as a target.
Does this help?