I have knee arthritus can i still play sports.should i wear knee protection?

You can play, but...: You can continue to play your sports as long as you can tolerate the pain and discomfort caused by the arthritis in your knees. If the pain becomes too bothersome, you could try corticosteroid injections or hyaluronic acid injections into the knee. Arthritis is an internal inflammation of the joint, so wearing external knee braces won't do anything to alleviate your pain or protect your knees.

Yes: Its great that you are maintaining an active lifestyle. Depending on your weight and strength, some sports will be more comfortable than others. Avoid sports that twist or jar the knee. Don't start with running until your strength, flexibility, and shoe choice makes elliptical training comfortable. Jogging/cycling/ golf are easier. Use a wrap to keep the joint warm, not to protect from harm.