What a stupid post. The force applied by one body on another is equal to the force applied by the other body on the other, during the collision. There is no net external force. There is a massive impulsive force each body experiences due to the collision. No one said acceleration is not involved. It is involved in the build up to the velocity. It does not matter if the velocity was built-up gradually as done by the pros, or by sudden acceleration before impact (which is not how the pros do it). The misconception arises because some people mistakenly teach that the pros swing abruptly hard just before impact, despite tons of evidence to the contrary. To support their theory, they insist on talking about acceleration at impact. Their knowledge is as poor as yours, and like you, they don't want to correct it either.