It's hard to believe that this look didn't catch on. You might have to click on the image to get a closer look, but Gary Roenicke's batting helmet is adorned with a football-style face mask on the left side of his jaw. It was a temporary precaution that was taken after he was hit in the face with a pitch. There's a clearer shot of the makeshift guard here, and an excellent article by Uni Watch's Paul Lukas here. It largely focuses on former Pirates outfielder Dave Parker; to be fair, his helmet stylings were much more terrifying and unusual than Gary's.
What's your favorite unusual uniform modification? Brooks Robinson's sawed-off helmet brim? Frank Robinson's extended stirrups?