Sure it protects against concussions, but a soccer player wearing one is akin to Barry Bonds wearing his armor to crowd the plate. It affords Martinez the comfort to go into challenges that are dangerous. I’m not sure I’ve ever seen another soccer player wear one, not saying there aren’t, but it’s telling that a guy who plays dirty and physical is wearing one.I know Martinez plays physical, but I wouldn't let a mouthguard be the evidence of it. Mouthguards are great deterrents for concussions.
Steph Curry is one of the few that wears one in the NBA, and I don't think he's accused of being too physical.