I played tennis for a couple of hours last night, which is typical for me. Played OK... felt fine. No falls or crashing into the fence. When I got home, my left shoulder (non-racquet side) started feeling uncomfortable. Within an hour I couldn't move it much without pain. I had a hard time sleeping last night, and this morning it still felt the same. If I am sitting motionless, it feels fine. If I bend my elbow joint, it feels fine. But, if I lift my arm at the shoulder in front of me or behind my I get a sharp pain that is localized in the front deltoid area. My shoulder is also sensitive to touch around the outside part of my clavicle, where it meets the shoulder. Again - no impact or even use of the left side yesterday... just tennis (and I am right handed). Any ideas? I am a little concerned it is a clot or something like that. It's the first time i have had what feels like a sports injury, but I can't identify what happened or why it would be injured.