Tripping 20 amp single pole breaker.
You may have already tried this but I am assuming you haven't. First disconnect the circuit from the circuit breaker. Make sure the breaker is reset and see if you can turn it on. Use a voltmeter or a non contact indicator to see if there is voltage at the termination. Now you know It's either the breaker or the circuit.

If the breaker resets and stays on, then examine the circuit conductor that was attached to it for it shorting in the box. Do a visual inspection will and look for a nicked wire, discoloration or a burned spot inside the panel.

Now check the circuit with an ohmmeter or a continuity tester to ground and see if you get a "ring". If you do it's the circuit and if you can't see where it is shorted in the panel then it is down line in the circuit and the moving of the breaker was just a coincidence. If you don't get a ring then connect up the wire and you are good to go. 

Also check the circuit and locate all of the devices that may be connected or plugged into a receptacle or if it is a light turn all switches to off while checking.

At this point your has been isolated and identified, now all that is left is repairing the damage.

Hope this helps and good luck