Just another case of Talking is a Free Action.
If a PC ever says they want to catch a live grenade... Well, of course you should let them try. Just be prepared to go into critical mop-up mode if necessary.
Catching a live grenade. Holding it. Catching a live grenade.
I know how the grenades that we use today work; pulling the pin doesn't start the timer, it's more of the safety. Letting go of the grenade starts the timer.
Somehow, this robot has fast enough reflexes to catch a grenade (okay), enough time to carry on a conversation, and still throw it far enough away to be out of the explosion range. Why are they using people if they have robots like this? Seriously. If you have battle robots this good, and we've already seen the droid factory technology, why do you use people at all?
Now, the dialogue. I thought you might need some help. Some help killing people. You can't cover the whole battlefield yourself. But I can. Just watch me. Let me show you what kind of combat droid I have. One insignificant toss, and I'll take out all of those troopers behind you.
What disadvantages did Sally take to get a robot that is this good at combat? Has Pete's min-maxing rubbed off? Will her "just toss death around like it was nothing" lead to part or all of the TPK?
And remember: this whole thing looks like a kill box. Whoever has been killing the soldiers is watching these people, and not killing them. I just imagine some people offscreen, reporting to their superiors, and saying something like "they would make a powerful addition to our side"/"they will join us or die".
I mean, it's not like these PCs are weak minded non-Jedi...
I've possibly mentioned this before, but I really like K-2.
Something I've noticed here is that Bria seems cool with killing people, K-2 obviously doesn't do anything except killing people, but Cassian is very much non-lethal. This possibly confirms that he doesn't really have a combat background, but it is certainly suspicious behaviour for him to be really concerned about not killing Stormtroopers when he is supposed to be in the Rebellion.
I hope someone mentions this soon. Maybe Bria. She does seem very good at killing people, and may get annoyed if Cassian keeps telling her not to do it.
GM: A trooper tosses a grenade at you.
K-2SO: I'll catch it. <roll> 17!
Cassian: What are you doing?
K-2SO: Just standing here.
Cassian: No, what are you doing with that grenade?!
K-2SO: Oh, I saw some explosions and thought you might need some help.
Bria: That's nice of you.
K-2SO: Some help killing people.
Bria: I'm pretty good at that already.
K-2SO: You can't cover the whole battlefield yourself.
Bria: That's true, but—
Cassian: That grenade's still live! Get rid of it!
K-2SO: You're the boss.