Are you giving your hoods weapons? Hoods with weapons will react to and join a fight. But most of them won't have high firearms skill and the AI sends out most people with pistols. The longer the firefight lasts, the more police will be drawn in and you can end up having a giant moshpit and 10+ dead hoods of all gangs over 1 hood taking one shot at another.
Keep most of your hoods unarmed, so they will simply run away. Police will not target them and often take out attacking enemy gang members. Much higher survival rate.
If there's too many attacks from an agressive gang and you need to reduce their numbers, find out where their headquarters is (many cars outside, always 1 guy standing still outside and 2 walking around the block) and post a dedicated killsquad there. 4-5 star skill in guns, armed with the $ 750 rifle, which is the best weapon period.
Then:
1 - Find police nearby, kill them.
2 - Take out the gang's 3 guards.
3 - Stand outside their HQ and click street order 'kill' on literally every person who comes near (can't kill civilians, it'll only work on gang members)
4 - After 2 murders your hood is wanted, keep them away from police until friday ends.
5 - Send wanted hoods to the pool for a few weeks and replace them
6 - Rinse, repeat, grind an enemy gang down over 4-5 weeks if you like. Making an extra headquarters near theirs cuts down the traveltime for your killsquad, which increases how many enemies you kill
