This is of course in the context of something being wrong with the boat. I'm just trying to work out some credibility issues in a fiction.
As everyone said, to free the prop from something wound around it.
I've found it effective to pull on the trapped line while working the transmission from ahead to astern, to avoid having to dive in the first place, so I suppose if you are looking for a scenario for an accident you could have someone in the water trying to cut a line signalling to someone in the boat to put it in astern and something going wrong like they guy getting his foot caught in the line.
Or the old movie trope about having to sacrifice someone because the boat is under attack, or there's a ferry heading right for it and they have to move to save everyone else.
Not usually unless you have been misfortunate to get something wrapped around the prop.
Try not to go near a prop whilst in the water and engine is running. Props are very efficient at cutting toe nails starting from ones head and working down.
Of course not while it is running! But what kind of sports boat are you talking about a I/O, a O/B, V-Drive, and we know it is not a jet due to a propeller.
when I had my O/B I always trimmed my engine up to the trailer position, so if I got rocked by a wake I did not get damage to my lower unit.
I also used my engine as a ladder to get back up on my boat during skiing. Of course it was shut down.
Something like a rope wrapped around the prop. Hitting something and checking the prop for damage. Usually the engine can be trimmed up and then the prop clears the water. You could check for most damage from inside the boat. You might have to get into the water to clear something wrapped around the prop.
Maybe the Rope from a lobster pod which the boat driver didn't notice, wrapped around the prop.
You would not do this with the engine running .
WE used to climb over the lower unit of an I/O (actually sit on the lower unit put your feet on the horizontal fins and stand up then use the lower unit like steps) after skiing to get back in the boat – often it was idling in neutral.
Hi all sorts gets wrapped around the propeller so yes you might need to untangle it. fishing nets and fishing line. even some other items like sails left hanging around. so it would be best if the engine was switched off so no accidents happen.
Tangles with kelp, weeds or fishing tackle. After the prop hits a rock or beaches on a sand bar.