The phrase "a guy competing" is correct and usable in written English.
It can be used to refer to a male participant in a competition or contest.
Example: "In the final round, a guy competing against the champion surprised everyone with his skills."
Alternatives: "a man participating" or "a male contestant".
Here's a little guy competing in the $17 billion Internet commerce market against the likes of IBM.
Just as Apple doesn't want to be in the generic MP3-player business, Blumer didn't want to be just one more guy competing to charge a few hundred dollars an hour to do your taxes.
Jimmy Fallon (a white guy) will replace Conan (still a white guy), compete against Craig Ferguson (a white guy), and then, at 1 35 a.m., pass the baton to Carson Daly (yep, a white guy).
He also wants to mentor young Latin players, to tell them to save the little money they make in the minors, to take care of themselves once they're mixed into a new country, then into a sea of guys competing on the same mission.
The winners of an Eddie Vedder Karaoke Contest in Telluride -- the lone female entrants among a group of guys competing last Wednesday -- enjoyed a bucket-list moment when they sang the chorus to "Daughter" alongside the iconic frontman.
Guys get traded off all the time, and also there's a certain competitiveness, guys competing for salary money".
In it this young Mr. Hollywood will choose from a group of guys competing to be his best friend.
Watch the… George Giove, a twenty-nine-year-old journeyman pizzaiolo (Italian for "pizza guy"), competes for the United States Pizza Team.
By Field Maloney George Giove, a twenty-nine-year-old journeyman pizzaiolo (Italian for "pizza guy"), competes for the United States Pizza Team.
George Giove, a twenty-nine-year-old journeyman pizzaiolo (Italian for "pizza guy"), competes for the United States Pizza Team.
