For the past two days, Pietro had gotten little sleep and had spent the majority of his time brooding. The anger he directed at the mugger didn't just have to do with Wanda, but he wasn't exactly coherent enough to realize this.
The man tried to get up, but Pietro was fast enough that the man didn't present a challenge. "Stay down, you fuck," Pietro all but spat, landing a hard blow to the man's cheek. He punched again, without much direction and the man let out a groan. The knife had flown out of the mugger's hand and was on the ground, closer to Wanda than to the pair of them. "You like to attack girls with knives?" Pietro kicked and the man shouted.
His attention was fully on Wanda's wanna-be mugger and not on his sister. Later, he might have some shame for his actions, but fully in the moment, Pietro was more wild animal than man. There were some instincts that were just too strong and protecting the one person he called family could drown out anything.