An ESC, or electronic speed control, is the electronic unit between an RC car's battery and motor that converts the receiver's throttle signal into motor power, and also handles braking, reverse, and low-voltage cutoff.
Racing ESCs are programmable, and the settings that matter are throttle and brake behavior, LiPo cutoff, BEC voltage, and timing. Hobbywing’s XeRun XR8 Plus G2S manual describes a default LiPo cutoff derived from the detected cell count at 3.5V per cell, a switching BEC adjustable from 6V to 8.4V, and up to 48 degrees of boost and turbo timing. That timing range is exactly what spec classes rule out: they require “blinky” or zero-timing mode, shown by the ESC’s blink code — but the code alone isn’t proof, so ROAR also approves specific firmware versions. Watch ESC temps after a run — thermal shutdown mid-main is a gearing problem, not bad luck.
The ESC decides how the car puts power down and whether it finishes the run, and running non-approved firmware in a spec class gets you tossed at tech.