What you might have known is that Adrian Beltre (pictured, in happier times) suffered a severely bruised right testicle (OW! OW! OW! Noooooooooo!) in a recent game.
What you almost certainly didn't know is that 29 years ago, another Seattle Mariners player suffered the same fate -- against the Twins' Roy Smalley, no less. We have an unconfirmed suspicion that it wasn't actually a line drive, but rather a graze from 60 feet, 6 inches by Smalley's massive hair, but we'll let the Seattle Times do the heavy lifting:
Two other notable elements from 1980: Mike Parrott won on opening day for the Mariners and finished the season with a 1-16 record (and a ruptured testicle after getting, uh, beaned by a Roy Smalley smash; but that's another story).
A colleague alerted us to that Smalley-Parrott play and said he was at the game when it happened and that it was obviously not a pretty sight.
All of this is a long way of saying: why on earth would a player not wear a cup?