In reply to AlanLittle:
> Bot to answer the original question - *very* special case technique for runout routes. Makes a harder catch and puts more strain on the gear,
I think the hardness of the catch is very much a secondary consideration if there's serious doubt about whether the gear is even going to be weighted before the leader hits the floor.
Actually, I would say that dynamic belaying should be very much the exception for single pitch trad climbing. Yes, occasionally you can use it to kill a big swing, or to get someone below an overhang they would otherwise hit but you need to be absolutely certain you have the airspace to get away with it. If you
really know what you are doing, maybe, by agreement, to try to spare a particularly marginal placement but this is complicated stuff because if you miscalculate you'll end up with a leader who has fallen both further and faster because you didn't stop them accelerating soon enough.
We have stretchy ropes to take care of the catch (which of course means that people fall much further than they are expecting anyway). As a belayer your job is to avoid the hard stop at the bottom. If that means stepping down, jumping down or, at a minimum, crouching, then that's what you do. You should have thought about what you are going to do before it happens. You are aiming just to take in slack and should avoid ending up both weighting the rope but that depends on how fast your reactions are and how fast the fall is (sliding down a slab can be surprising slow to start with).
As with so many things in life, timing is everything. No leader is going to thank you for going too soon.
I'm aware that sport climbing is different for all sorts of reasons but mainly because a ground fall should be impossible.