What Causes Dark Spot On Arm?

I am male,age 29 . Last week played lot of cricket and then went to swimming - causing lot of stress on my right shoulder and upper arm. Next day realized some dark big spot on the upper arm region ( black & red - similar to blood clot) and some pain moving the hand up and down. I am doing daily workouts for the past 2 months. Its just because of extra strain bowling with right hand. What is the reason for the dark spot and how to cure it?