a foot fault called on you from across the expanse of the tennis court would've to be pretty flagrant..and therefore should be. i doubt i would call it though..unless it was very obvious and the guy was killing me on his serve.. i play a guy who often starts his motion with toes over the lone.. i never say a word because his serve is not booming and i'd rather his go in as opposed to hitting softer or slowing things down further with more second serves..
I had a guy that went 2 feet inside the line. We were playing doubles so it was super easy to spot (though if we looked for it from the baseline, we could probably see that too). The guy seemed surprised as if we were trying to cheat him out of a point, which blew my mind since he was mindful of being right behind the line before starting his motion then took a very deliberate and large step into the court during the toss. Found it funny when he was surprised again when we called it on him the second time we played against the guy when he didn't learn his lesson.
Competitive doubles, I will call that stuff. But the thing is, unless you're blatantly crossing the line, I'm not calling it. If I'm looking for it, which would mean I know they're coming consistently and obviously, I'll call them every time. If it's something like a quarter of the way into the line, that's too close and I won't bother. Half is easier to see, completely on the line I will look for them every time. If you aren't going at least halfway, I wouldn't even notice the first time to keep you honest.
Friendly doubles, I won't call it unless you're crossing sidelines (which I'll tell you before you start so you don't actually lose a serve). If you deliberately cross the line excessively, I will call you out, tell you to stop chimping out, and have you hit the serve again. But as long as you don't go more than half a foot inside the line, I don't care.
In most cases, if you're foot fault is obvious enough to get called, you deserve getting called out. Most people who do foot fault consistently are pretty reasonable (I don't like it, since I'm very deliberate about giving a centimeter or two of space to ensure I'm not foot faulting, but I can understand that not everyone knows exactly what their feet are doing or where they are; that being said, you should be able to know when your feet are well inside the court).
