Can the opponents call foot fault?

Answer 1

It depends on what level of game. On the pro circuit (i.e. the ATP or WTA), opponents cannot call foot-faults. Additionally, there are baseline judges who are there to call foot-faults just as there are judges on the sidelines to call the ball out. However, when there are no umpires (in lower level junior tournaments), a player can warn his/her opponent that s/he is foot-faulting, but then an official must be brought down to make an official call on the next observed infraction.