My index finger got caught in a baseball glove. i had instant pain and today its knuckle is purple. i can't bend it. could it be broken?

See an orthopedist: Particularly one who specializes in hand surgery. This is not likely to be broken, but you will probably need imaging studies. May have dislocated a joint, sprained or strained ligament or tendon, etc. Go and get seen and hope you are better soon. Not funny at all.

Possibly broken: You need an evaluation for possible tendon injury vs bone fracture.

I agree: With your mechanism of injury and bruising, an x-ray would be an appropriate choice. See an orthopedist asap!