Sudden bump on wrist?

Earlier today I was skateboarding and fell. When i got up i noticed that there was a bump on my left arm just below the wrist joint on my pinky finger side. I compared it with my other arm/wrist and the left one was much bigger. It is hard and bony like just wondering what it was. I have looked into ganglion cysts but not sure if that is the case because i haven't seen anything on the internet about it being in that spot.