D&D 5E so a crocodile and a pc fighter go into a grapple ...

[The Grassy Gnoll]

I'd say rule each situation on its own merits.

Initially I thought, rule that Piercing weapons can be used - but then I thought, morning stars? And as longswords in 5e are all classed as slashing weapons wouldn't it be possible to envision a cut across the grappler's back or thigh as it slices as opposed to stabbing, so slashing should be ok too. Then I thought two handed weapons might be useless. And bludgeoning. Then I thought bludgeoning could still be used to smash him round the back at his head, or hit his kneecap, etc. But then once I scooped up all the worms and put them back in the can, I thought, they're at disadvantage so that accounts for the difficulty in getting a decent hit in anyway without over complicating things.

In the croc scenario, it's less of an "aggressive cuddle" set up than a regular grapple, so a swing at the creatures head should be doable.

In summary...no. Go for it. But I do think a two handed weapon would be pretty crappy in close quarters, realistically. But then again...oh god I'm overthinking it now. It's D&D, you can narrate a way.

 

[The Grassy Gnoll]

Scratch that, I was thinking grappled = Disadvantage.

That's wrong, it's Restrained.

So...you could then, if you wish, rule that certain weapons could be at Disadvantage when grappled. Though a grapple can be:
- a neck choke
- a leg grab
- a midriff grab
- a shoulder grab
- an attempt at a half nelson
- a hand/arm grab
- from behind
- in front
- from the side
- made by a constrictor of some sort (wrapping around)

...so any weapon could feasibly be used somehow to make some sort of damage to your opponent in a 6 second chunk of time. Hence why no disadvantage.

Unless they're restrained, of course.

 

[Unwise]

edit: video here showing how you end up prone (arm not leg to be fair), but a shove ain't gonna cut it either way http://youtu.be/6ZhHHVsAnI4

Not cool man, put a warning on that. I don't need to see someone's arm do that. It starts off looking educational.

 

[spectacle]

Anyhoo, if I understood you correctly, did you imply that a PC shouldn't be able to use a medium-sized weapon for an attack when grappled? And only be able to use daggers?

A cool houserule would be that attack with daggers don't have disadvantage for being Restrained or Prone. That would finally give adventurers a good reason to carry daggers instead of just using their longsword for everything.

 

[The Grassy Gnoll]

Not cool man, put a warning on that. I don't need to see someone's arm do that. It starts off looking educational.

Sorry - I thought it was pretty obvious that something unpleasant was going to happen, as it builds up for long enough. My bad.