Ichiro Suzuki has been cited. (In Japan he would be Suzuki Ichiro, but the principle is the same; Suzuki is his family name, Ichiro his given name.) Chili Davis, a pretty good player for a long time, wore “Chili” on his uniform. Both players have notably boring and common surnames (Suzuki is the second most common family name in Japan) so maybe that’s why they went with first names.
Vida Blue wore “Vida” for at least a good portion of his career.
The Official Rules state that a player must wear his last name, unless given specific permission by MLB. I’m not sure when they came up with that rule. Ichiro had worn the name Ichiro in Japan (why they wear their names in Roman letters I don’t know) so asked permission to do so just to keep things the same when he joined the Mariners.
Ichiro means “Number 1” or “First born” in Japanese and is used as a given name for boys. So, I think, Ichiro Suzuki used it on his jerseys in Japan and here in the U.S. as a play on being number one!
I’m rather certain I’ve seen them with first initials, I imagine that in cases like the Mets’ one mentioned earlier, they could put a middle initial as well.
Chipper Jones and Andruw Jones wore “C. JONES” and “A. JONES” for a few years. Eventually everybody acknowledged that the initials weren’t needed to tell them apart.
Steve Smith Sr of the Baltimore Ravens has a similar setup. At least Bradley has been a Junior all his life. Smith didn’t become a Senior until his son was born.
I would assume the same mysterious reason Robert Griffin III’s jersey says GRIFFIN III despite the distinct lack of other Griffins on his teams. Nor, for that matter, were the previous two Robert Griffins professional football players.
But first names aren’t on the jerseys. There are plenty of Smiths out there in the NFL. Heck, there have been three Gronkowskis playing recently, but no one needed to identify them individually.
In the case of Steve Smith (Sr.), Robert Griffin III, etc., I suspect that it’s entirely a matter of the player’s personal preference (perhaps related to pride in fatherhood or family ties). In the NFL, in particular, it’s been in the past few years where we’ve seen the not-technically-necessary additions to the names, and given the NFL’s utter lack of a sense of whimsy, and a strong desire for uniformity, I’m more than a little surprised that they haven’t created yet another rule about what can and cannot be included in a player’s name on their jersey.
Seven years ago, MLB had a pitcher and a shortstop both named Tony Pena. The latter - Tony Francisco Pena, son of veteran catcher and former Royals manager Antonio Francisco Pena - had Jr. on his jersey even though “Jr.” is not part of his legal name.
Merle and Phil Olsen both played defensive tackle for the Rams in the early 70’s side by side. Their jerseys just said “Olsen” and their numbers differentiated them. First names really don’t enter into it, there’s no need to differentiate them besides their number.
I’m coming at it from an announcer’s perspective. You got two guys with the same exact name (first and last), is it easier to say “Smith Senior” or “eighty-nine”?
Red Sox pitcher Robbie Ross Jr.'s wife refers to herself as “Brittany Ross Jr.”, as if “Jr.” is part of Robbie’s last name. The Red Sox TV announcers sometimes say “Bradley Jr.” and “Ross Jr.” when they refer to them without using their first names (not that saying “Jr.” is required then either), but they have been getting better at using just “Bradley” and “Ross”.
