The first offence is Ashton breaking law 10.1d (obstruction) by blocking Watson's pursuit of the ball. It's clear and obvious from the early shots, but less so from the later replays. Those saying this is permissible if he 'holds his line' are misinformed or thinking of basketball rules. The second offence is potentially Watson breaking law 10.4e (dangerous tackle). It's for the referee to decide whether the illegality of Watson's challenge was due to Ashton's illegal block. On this occasion he decided against Watson. One can understand Watson feeling aggrieved, as he seemed to have his eyes on the ball when Ashton blocked him. However, the two distasteful aspects are the reactions of first Ashton, who is a class A turd for blocking then trying to influence the ref with his protest, and then sadly Watson for being petulent. For me - two yellows, but what do I know - I haven't reffed much at elite level.
Agreed about the defensive issues. As a union winger you're part of the back three and need to cover as a fullback with all the game understanding and awareness to read the match and be in the right place at the right time. This is Ashton's major weakness.