[Nemo]

I think we are stuck with subjectivity in foul calls, because the alternatives are worse. I think the best set of rules would advise the referees to mostly let the teams play, but call fouls if the contact becomes egregious in the judgment of referees.

Here are some worse alternatives that eliminate the judgment calls:
1) Any type of contact is legal: results in battle bots
2) All contact is illegal: robots tiptoe around each other in fear of penalties, creating a lame game
3) Any contact within frame perimeter is a penalty on the extending team: penalizes offensive robots more, and allows teams to ram other teams to give them penalties
4) Any contact resulting in damage is a foul on the other team: pretty silly if you were sitting still and a team runs into you and breaks themselves, or if their robot was held together with bubble gum and a really light hit made their widget fall off.
5) Any collision faster than, say, 10 ft/s is a foul on the team that initiated it: how do you know which team initiated it, and how do you measure the speed? Better to simply admit that collision speed and intent are judgment calls on the part of referees.

Regarding the fouls for possessing the other team's game ball, I think the rules aren't hugely far off from where they need to be after the update that allowed regular fouls for inadvertent possession. The point value of fouls and technicals is still very high compared to the average match score, but I think it is appropriate that referees can award different penalties depending on the perceived intent and result of an opponent possessing your ball. The existence of that technical is important to eliminate any incentive to intentionally possess the opponent's ball and take the penalty. I think the smaller foul is helpful, because if the other team possesses your ball by accident, it still wastes some of your time. Other sports have different penalty levels, too: Hockey has major and minor penalties, basketball has "flagrant" fouls, football has 5 yard and 15 yard facemasks depending on severity, etc.

Last comment: I think games would be called better if the "can't cause your opponent to commit a foul" rule was consistently followed. The other team can't throw a ball into my stationary robot and give me a foul, and they can't ram their lego tower into my robot to break themselves and give me a foul, and so on. This is another judgment call, but it's a necessary evil to prevent other problems that are much sillier.