To trundle (a boulder):
In climber terms means to gently assist gravity in setting a large stone in motion.
This is occasionally done to clear a climbing crag of potential future rock fall.
It is potentially very dangerous both to the trundler and anybody the vicinity of the trundling act.

It is not a good practise to get into unless highly warranted
If you feel that trundling a potentially dangerous rock is justified,
make sure you take great precautions to look for and warn anybody below.
Even a marble sized fragment that ricochets can become lethal.