It's a non-contact league so any obviously jamming or physicality is a foul. You can slyly place a hand one someone as long as you don't fully extend but we did have one game (out of the many) where a ref said both teams were being to handsy.
As someone who is super out-of-shape, this is fun for me and I can tell that I'm more capable as the season progresses but it's mostly about the practice sessions.
As a defender, you are allowed to occupy a spot without having to cede ground to the receiver. If they run through you it would be a foul against the offense but they factor in size and gender on those plays. If a smaller guys runs into a larger person, they probably won't call any fouls.
Practice every Saturday; you're always welcome to join.