According to the atlantic:
Grey squirrels are statistically more likely to attack (or bite) humans than red squirrels, primarily due to population size, range overlap with humans, and bolder behavior in urban/suburban settings. Exact ratios are impossible to determine reliably because attacks are extremely rare overall and not systematically tracked.
https://www.theatlantic.com/science/archive/2017/06/when-squirrels-attack/531129/