For the most part, I don't really get Munin's objections.
The only difference I see is in the stakes Paul. A grapple is a narrative tactic for delaying, not resolving a situation. It could potentially resolve it, but TIME is what the act under fire was buying. If the guy inside the house wasn't going anywhere, it wouldn't mean a damn thing.
If the PC was backed into a corner by trying a bunch of other stuff, maybe you needed to let that snowball roll further before giving them the next "what do you do?" Maybe he should have been inside and be swinging something at the other one, and the PC is now rolling act under fire to drive tackle him. i.e. Under the threat of the other guy getting beaten up, I try to hold the aggressor down. On a hit, the other guys gets away. On a miss, he doesn't. On a 10+ and I or the other guy also didnt get whacked with something mean.
However, that doesn't take into account the table dynamic we had at the time, which was the PC already trying a few things which didn't work, and now being backed into a corner: she had to act NOW or it would be too late. This meant that all the players were looking at me, implicitly asking, "Can she do it [perhaps fast enough]?
This just makes me think you might have been babying the situation. It happens sometimes, you pause before you should have, you give them a chance to say something, and whatever they say doesn't seem like it'll work. It's okay to say it does not. If she's not willing to hurt him, and she doesn't have some distinct skill in this type of take down, or maybe she's just too small by comparison for it to be realistic, maybe she just gets smacked into the dirt, or grabs a hold, but it pushed off while he breaks into the door, and you carry the sitch forward until you HAVE the stakes you feel comfortable with.
If you don't think what she says will work, tell her that's not enough to stop him. A pipe against the throat? Unless you're planning to hurt them, that pipe is in your way.
Maybe, you roll cool anyway, and on a 7-9 she is grappled by him. 6 she is tossed aside groaning and he's got the other one. 10+ phew. I dont like this much because the 7-9 doesnt mean much unless he's going to threaten her. If he just lets go and goes back to the door, the roll didnt change the sitch, and that's a good example of a roll that should not be made.