Simple question here, that I'm quite sure will come up in my campaign relatively soon, so I want to head it off at the pass: How would a PLEC (Private Law Enforcement Company) like Knight Errant or Lone Star react to armed action by a Megacorp like S-K or Renraku going off their private property to perform armed action, such as retrieving something stolen by Runners?
Company Men (corp shadowrunners) are semi-deniable assets used for Just This Sort Of Thing. Show up at the exchange, shoot the runners, kidnap the Johnson and get their stuff back? Sure. Do it as quietly as possible?
Absolutely. Remember, unless it's immediate hot pursuit -- and even
that can get dicey for even a megacorp -- the law of the corporations is 'don't
provably shoot the place up'. As has been pointed out, this is why they hire shadowrunners, through three layers of deniable assets.
To get back to the 'hot pursuit' angle, the short answer is: Depends. Is the corp you just hit (Ares) in good with local law enforcement (KE)? Is there some friction (Saeder-Krupp)?? Or are they sworn enemies (Lone Star, Aztechnology)?? Understand that any collateral damage able to be provably laid at the pursuing corporation security forces' feet is going to cost the corp money, and if the local cop corp is feeling even vaguely pissy (they usually do, because being pissy on the side of the citizens will increase their approval rating, making keeping the multi-billion-nuyen contract easier), they will do all they can to provide that evidence. 'Oh, sure, those shadowrunners did some damage, but your cars smashed up
thirty five others and caused over five million in property damage. Pay up.'
This is why having Inter-Corp Politics as a knowledge skill is a Good Thing. An example in a previous edition (SR2?) had a runner team running like hell from a Knight Errant team after having hit a site whose security contract was 'up for renegotiation', and crossed into territory patrolled by Lone Star. LS pulled them over, they quickly explained the situation and basically offered a bribe to the Star. The Star told them to beat feet, then got into the KE team's face to demand what the hell they thought they were doing, driving around at high speeds in THEIR patrol area. Know the
political lay of the land, and it's entirely possible that the guys who should be stopping you will become your temporary best friends, just to tighten the screws on the people you just messed with.