CatNBox's Things

Okay this is a bit of a long shot since I barely remember the plot… I had it saved to read it later and lost it.

Essentially, the main character (maybe a college student? Might be graduated already) is introduced to boxing through his friend and it becomes apparent early in the story that he has a lot of experience in fighting already due to how quickly he learns. His friend who already does boxing introduces the main character to his boxing club he excels more than anticipated before his first fight.