If so, what sport, in what capacity, and what was your best result?
I’m not really expecting John McEnroe or Larry Bird to respond, but their are a lot of sports out there.
My Father was a boxer on the old Carnival Circut, back in the 50s.
Technically, according to USGA Rules, I am a professional golfer as I have accepted cash for renumeration for playing in golf tournaments.
If I were to have a handicap, it would be in the low single digits. It is not even close to the levels Tiger, Lefty and others. They would beat me by several shots on their very worst days and my very best days.
I have played with mini-tour players and I would have a hard time beating them on their very worst day and my very best day.
Of course, I only play golf twice a week and I never practice.
If chess is a sport, I’m a professional. 
Not a sport, but a game. 
I drove in a NASCAR touring series 21 years ago, it was at the time 2 steps below Winston Cup. I competed against Mark Martin, Harry Gant, Neil Bonnett, Chad Little and Bobby Allison.
Current NASCAR star Greg Biffle was a young buck upstart that ran in the Northwest series a few times that year. I made a bit over $9000 in purse money and finished in the top 15 in the point standings. My best finish was a 3rd at South Sound Speedway and my biggest payday was at Portland International Raceway. We were one of the support races for the CART series race.
Unfortunately for me, it cost about twice what I made to run the series and without a full time sponsor, I had to sell everything after the season. I even put race car driver on my tax return the following year for my occupation.
I played minor league baseball, rookie league and class A, a long time ago.
No, but I was a co-worker and friend of former Detroit Lion Homer Elias, who was pretty good in the NFL from 1979-1984 or so.
He was a nice, nice, big guy who died way too early.
Here is his Wikipedia article, which does not even include his death date, which I would add if i could remember. It must have been about 4 years ago(heart attack).
A cousin of mine is a member of the baseball hall of fame. He’s a name you’d know. Too bad I didn’t get any talent.
Cool. Who?
If by professional you mean simply being paid to play, then technically I am a former professional hockey player.
A former employer paid me for my time while I was playing in a men’s league for four seasons (and three summer seasons) … I’m still playing in that same league, though no longer employed with the same company. I play on my own time now, same as before I worked for that company.
I am not, but I work with two former NFLers and a former AAA baseball player.
Both football guys had relatively short careers in the NFL, but one went on to play in the AFL for a while. One is a history teacher and former Redskin, the other is a Phoenix cop who does security at our campus when off-duty and played for the Bears and the AFL Arizona Rattlers.
The baseball guy is our baseball coach, and he played in the Royals, Mets, and Red Sox (I think) organizations.
Our girls’ basketball coach played in an NAIA Women’s Championship basketball game.
That’s him. Well-known second baseman. 
Perfect.
What’s on second!
Wait a minute. First-baseman, surely.
I sorta wish I hadn’t noticed that. It was too good a joke to fall prey to nitpicking.
Sadly you’re right. I shoulda checked. 
To be real pedantic about the nitpick:
You should have said above “First-baseman, naturally.”
Although, I guess Shirley could be a name for a first baseman.