4th Metacarpal injury, I was taking the dog for a walk and had to pull on his collar a bit to get him up some stairs and when I released the collar I noticed that the ring finger on my right hand was "stuck" in the clasped position and would not straighten out. Is this an emergency or do I just need time to heal?

I would go see a doctor about this, it could be serious, but could just need be exercised through its normal range of motion. Hard to say and I don't want to suggest anything that could harm or damage your finger.