Final answer:
The ATP-CP system is needed for running up a 100-yard hill as fast as possible.
Step-by-step explanation:
The energy system needed for running up a 100-yard hill as fast as possible is the ATP-CP (ATP-creatine phosphate) system. This system relies on stored ATP and creatine phosphate in the muscles to rapidly provide energy for short bursts of intense activity like sprinting. It does not require oxygen and can supply energy for approximately 8-10 seconds.