I'm using the ones in Hall of Judgment. It's basically like this:
You attack with your grappling skills, and inflict Control Points based on your thrust damage. The more control points the target has, the bigger a DX penalty they get to do anything. You can spend inflicted control points to make opposed tests against your target easier and do several other things. If you're grappled, you can try to counter-attack with a grappling skill to remove those control points, subject to the DX penalty.
The slime inflicted 15 CP on Madoc. Since that's higher than his ST, he has -16 to DX: he's pinned. It's up to you to save him. You can try to attack the slime with weapons, grapple to try to pry it off the cleric, or whatever else you want to try.
I apologize, I missed the message when processing the attacks. It's quite likely you would have gotten a solid hit, though Bob would still have been the one to finish the monster off. We can go with that narrative in the IC thread.
I feel some clarification is in order: The people at the top of yonder hill haven't noticed you yet. The ballista is covering the main street approach through the stairs and arches, but there are plenty of side streets around and you are free to plan an alternate approach, or ask me any additional questions you may have about your surroundings.