re: What is a foul in soccer?

I watched a little more intently today. From what I’ve gathered, it seems if you’re on the ball, they allow defenders to be very physical as it’s up to you to use your body to maintain control and deal with the contact. It’s fair game.

But when there is a play developing and a defender does something physical to prevent your movement as a player rather than playing the ball, it seems that’s awarded a penalty.

It’s just difficult because when I think I’m kind of getting it down, something that I think was a foul is a play on and something I think is a play on is whistled a foul. And I don’t know if those are just questionable calls/no calls or if I still don’t quite grasp the rules.