This column is worth reading in its entirety: From the New Criterion:
In his own era, matters were different. Baker was a famous, even legendary, amateur hockey player. He had the name recognition of today’s professional athletes. But there was an important distinction. Baker was the most celebrated hockey player of his day, not just for his skills on the ice (though those were extraordinary) or his strikingly good looks (he was known as “the blond Adonis”), but for his unwavering sportsmanship, civility, and good character, descriptors that are difficult to apply to today’s celebrity-athletes.
Baker was not just another sportsman. He was what many young men of his day aspired to be: a gentleman athlete. In an article about Baker published in 1991, Sports Illustrated explains that the old code of sportsmanship involves being “modest in victory” and “generous in defeat.” The gentleman-athlete “credits his triumphs to teamwork, accepts only faint praise for himself. He is clean-cut in dress and manner. He plays by the rules. He never boasts, for boasting is the worst form of muckery.”Hobey didn't want to be paid, and they seem to count that as "gentlemanly" here. If you throw out that criteria, I might suggest: Joe Mauer and Peyton Manning, and then nobody jumps immediately to mind, though I'm sure there are.
Perhaps another way to think of gentleman athlete is: Would you approve of your daughter dating him?