Q: Context: The flank strap is a rope made of a soft cotton rope at least 5 / 8" in diameter is acceptable as a flank strap and does not require extra padding with sheepskin or neoprene. It is tied around the bull's flank. Contrary to popular belief, the flank strap is not tied around the bull's testicles. This rope is to encourage the bull to use its hind legs more in a bucking motion, as this is a true test of a rider's skill in maintaining the ride. If it is applied improperly a rider may request to ride again, as the bull will not buck well if the flank strap is too tight. The flank strap is applied by the stock contractor or his designate.

Question: where does the flank strap go on a bull?
Let's give stream of consciousness below
The relevant sentence in the passage is: It is tied around the bull's flank. So the answer is around the bull 's flank.