Mine was probably basketball because I wasn't able to get much better despite playing pretty frequently. I was good with effort which allowed me to be useful defending and rebounding. Beyond that and brief spurts of hitting jumpers for a two minute span (with a three week wait in between spurts), I wasn't good.
I was worse at tennis but at least have the excuse of not playing a lot. I could never get the hang of serving.
Is pool a sport? If it is, that would be my worst. We had a nice table in my college apartment and decided to keep standings. There were four of us and we decided to play each other thirty three times each to end up with ninety nine games each. Is 2-97 a good record? I had one legitimate win and another time when my opponent scratched on the 8 ball. My roommates were all good players but 2-97 is 2-97.