Groin guards are essential equipment for protecting you when that inevitable errant blow happens. It is one piece of equipment you should never be without when sparring.
Groin protection for mixed martial arts comes in two basic types: Stand-up and grappling. Stand-up cups offer a larger protective area and are better when that errant blows hits the mark. Grappling style cups are sleeker and allow unrestrictive movement when ground fighting while still providing effective protection. Choosing which one to where just depends on the activity for the session.