First one was very harsh, imo. Ruck for ASM, Hines makes the pass from the breakdown (playing SH) and Stoddard was "repositioning" himself in a way to disturb Cerlmont's attack. The ball came his way, so he took it and attacked. Definitely a penalty, but I don't think it deserved a yellow.
Second one, Sivivatu breaks away on the wing (stepping on the touchline, one might add) and after some crazy play he is brought to ground 2 metres away from the line by Stoddard. Then, Stoddard makes everything possible for the ball not to go out quickly. In particular, he positions his legs on Clermont's side of the ball (in a very unnatural way, and a few seconds after the tackle, no "inertia" here). Deserved yellow, definitely.
Scarlets have been playing some dodgy tactics all game. They keep the ASM players on the ground after the tackle so they can't rejoin the attack. They target Parra specifically, they did it to him at least two times, which slowed the ball exiting the breakdown the next phase. Plus, they were realy taking their time when Stoddard was on the bin, to take the lineouts for instance.
Penalty try as I type. Well given, in my view.