Kinda complicated but its got me worried pleaze help.?

okay on my right arm there is a "squishy spot" i guess or not as muscular as the rest of my arm because i used to swing in a rope swing alot and i would lean up agianst it and something happened to that area so i was just rubbing it and i felt a small little ball move. Is this dangerous omg its got me freaked out! help asap!!!