The word(s) "back" appears 101 time(s) in 98 verse(s) in Quran in Muhammad Pickthal translation.

(11) Say: O People of the Scripture! Why drive ye back believers from the way of Allah, seeking to make it crooked, when ye are witnesses (to Allah's guidance)? Allah is not unaware of what ye do.

(12) Muhammad is but a messenger, messengers (the like of whom) have passed away before him. Will it be that, when he dieth or is slain, ye will turn back on your heels? He who turneth back on his heels doth no hurt to Allah, and Allah will reward the thankful.

(13) O ye who believe! if ye obey those who disbelieve, they will make you turn back on your heels, and ye turn back as losers.

(14) Lo! those of you who turned back on the day when the two hosts met, Satan alone it was who caused them to backslide, because of some of that which they have earned. Now Allah hath forgiven them. Lo! Allah is Forgiving, Clement.

(15) And (remember) when Allah laid a charge on those who had received the Scripture (He said): Ye are to expound it to mankind and not to hide it. But they flung it behind their backs and bought thereby a little gain. Verily evil is that which they have gained thereby.

(16) How can ye take it (back) after one of you hath gone in unto the other, and they have taken a strong pledge from you?

(17) What aileth you that ye are become two parties regarding the hypocrites, when Allah cast them back (to disbelief) because of what they earned? Seek ye to guide him whom Allah hath sent astray? He whom Allah sendeth astray, for him thou (O MUhammad) canst not find a road.

(18) They long that ye should disbelieve even as they disbelieve, that ye may be upon a level (with them). So choose not friends from them till they forsake their homes in the way of Allah; if they turn back (to enmity) then take them and kill them wherever ye find them, and choose no friend nor helper from among them,

(19) O my people! Go into the holy land which Allah hath ordained for you. Turn not in flight, for surely ye turn back as losers:

(20) Nay, but that hath become clear unto them which before they used to hide. And if they were sent back they would return unto that which they are forbidden. Lo! they are liars.