Disclaimer: despite him clashing with John Terry at the Camp Nou in 2012 and being generally kind of dive-y, I'm a huge fan of Alexis Sánchez. He's a world class inside forward and I've adored him since he was at Udinese. That said...
... here is video of him punching Branislav Ivanovic during Chelsea's 2-0 win against Arsenal on Sunday, which everyone, including the referee, appears to have missed during the match.
Sorry, Sánchez, but that looks like a clear-cut case of violent conduct to me. There's a clash as Ivanovic tackles him, which is probably enough to provoke the Chilean to throw really bad hook at the back of the right back's head, and then fall down.
Obviously it wasn't hard enough to do any damage, but that's probably due to Sánchez's choice of target -- punching a bear has never done anyone much good (maybe he should have tried biting instead). Regardless of whether or not Ivanovic felt the blow very hard, this seems like footage the FA has to review. A three-game ban seems in order right about now.