Really? Define "serious" in quantitative terms. How about offensive or provocative. How many newtons? What surface area? What duration? What coordinates on a person's body? Your own quote says "normal person".

But fine, I will join you at this inane echelon of ticky-tacky legal sophistry. The cop who "assaulted" Don Lemon has not been found guilty by a jury of his peers. Ergo, he has not broken any laws, though he may be suspected. Ergo, he has not yet legally assaulted anyone.