Crossing the “line” was a frequent thing.
An acquaintance was a Korean War vet who flew P51 Mustangs.
He related a number of stories about flying combat in Korea.
He described how they were assigned to flying ground support and attacking bridges, railroads and trucks on highways. Frustrated by rules of engagement and watching the migs attacking B29 bombers at high altitude, they (P51’s) after dropping ordinance would loiter and wait for the migs to return to bases. They would follow them and empty their .50cal machine guns!
He claimed shooting down a half dozen and of the several that ejected, or he could see as he over flew them, every one was a blond headed Russian!
The weakness of the Migs was limited fuel quantity and pneumatic flight controls that used a non-replenished (in flight) air charge in a scuba like air tank, and limited ammunition stores.
But; they were fast, agile, and dangerous.... till they weren’t.