whatever you do in a fight, - you must NOT cruise, no matter what. the second you cruise you are retreating. - one single shot on the other person is to be considered re-engagement. when you cruise, you cruise OUT OF the system.
we had the situation with fighters against slower ships - and the general answer was "tough luck". a gunboat cannot thrust as fast as a fighter. and a fighter can fly more than twice as fast as a battleship. a fighter is considered retreated when he left the sensor range, in terms of thrusted away.
shield running happens in various situations and is widely accepted. whenever two ships attack one, you can be sure that the two ships will take turns in shield running. and thats accepted - when a ships shields is low, it usually falls back to regenerate while the other one leads the attack. - so shield running is accepted and allowed in the circumstances ( and the general answer from the community is : "dont fly alone" )
so when a single gunboat is attacked by a fighter - it brings enough firepower and protection to deal with the fighter - but it won t bring enough flexibility to finish the fighter off unless he breaks the rules.
whoever cruises first looses the fight <--- thats the easy rule, and there is absolutely no discussion about how much this is logical or not. if someone feels nasty that day - the one that cruises to catch up and resume firing on the target can be reported.