Asking for help after someone plays cards against you
 

Hello! I just had a fun evening with Super Munchkin, but we had a little discussion for a rule.
I decided to fight alone against a lv10 monster. One of my opponents played a +5 to the monster, so AFTER he played the +5, I asked the other player to join with me in the fight, for 2 treasures.
The question is: is it legal to ask someone to enter the fight together with you AFTER the start of the combat and after someone interferes in it?
Or first you ask if someone wants to join, and then the fight starts and other cards can be played to help or interfere?
Thanks in advance

Re: Asking for help after someone plays cards against you
 

You can ask for help at any time that you're losing the fight, as long as you don't already have a helper.