In JW-world, you only have 3 "legitimate" reasons to separate.
The elders, and no one else, decide if your separation meets one of those 3 criteria.
If they determine that it does, you are in "good standing". If they determine that it does not, then you are not in "good standing".
From the August 2016 "Study Edition" Watchtower, page 16 (I added the numbers to make the "magic 3" reasons stand out):
Separation might at times be justified. (1) Willful nonsupport, (2) extreme
physical abuse, and (3) the absolute endangerment of one’s spiritual life
are exceptional situations that some have viewed as reasons for
I.e. it is up to the elders to determine if non-support is "willful", or if the physical abuse is "extreme", or if the endangerment is "absolute".
Evidently, beating your wife is OK so long as it is not too "extreme", in the opinion of the elders.