Ultimate is non-contact. Non-incidental, play-affecting, or dangerous physical contact is not allowed. Non-incidental contact is a foul, regardless of intent, with various consequences depending on the situation and the league rules. Incidental contact, like minor collisions while jumping for the disc or running for it can be acceptable, depending on the circumstances. Parameters like who has the "right" for the relevant space, who got the disc etc. will determine whether a foul has been committed or not. Attitudes can vary between leagues and countries, even if the letter of the rule remains the same.