STX Stallion HD Arm Guard - Men's The Stallion HD Arm Guard is how to get top-of-the-line STX performance when you step on the field. It's constructed with dual-density High Def™ Polymer and a new fit system. Together, they bring an improved anatomical fit within the full-length, breathable sleeve. Lining the interior are silicone nubs to keep the guard from slipping as you move. Even more, this guard also contains odor-defense technologies. Sizing: M (for players 91-140 pounds), L (for players over 140 pounds).