We caught one that was trying to do that before the valve dropped. Pushrod length being wrong can cause the edge oth the rocket to hit the spring retainer. When this happens the rocker is pushing the retainer down and not the valve stem the same as a spring compressor tool would do.
If this is what happened then it will be easy to see if you watch the action from the side while turning the motor over.
With all that being said, often people try to blame the rocker arm when it actually broke after the valve stem gave up or a piston smacked the valve at high RPM's.