most fighters cannot adequately guards their balls!!
most fighters have bad stance.

when training together make it a "rule" that either person has the
right to "slap kick the balls"(snap front kick but gentle/fast)
whenever the other guy leaves the open for attack.

in this way you will both learn the awareness of your stance/line so
that you cannot easily be taken advantage of.

in self-defense... when opponent goes to strike your face/high:

one of two things works great wonders... lean away and snap kick his
balls

two of two things is to DROP TO KNEE and reverse punch or uppercut
the balls with palm or fist.

ONE is from distance out of his reach
TWO is within his reach inside his strike focus and under it... very
close. two can be followed up with trapping his leg and taking him
down.

NI