Your Hero MMR as stated in the Profile Skill Rating changes based on Custom Game Street Brawls

[kingofrock37]

I had green arrow up on Viscous before playing him and losing as a random hero in a Custom Game Street Brawl with friends, and now it's a red arrow down

 

[Goblin Man Sam]

This happened to me too! I was playing a street brawl with easy bots to test a mod I was making. Afterwards my skill rating for Infernus dropped a good amount. I had to do a double take and checked with steams game recording.

Before​	After​