doing something such as punching something is called the Kicking The Dog effect, and acts as a displacement.
However, this shows that people became more aggressive.
Thus, aggression cannot be entirely cathartic as it would be expected that doing nothing would build-up aggression and punching something would release it, yet this did not happen.
The central assumption - the idea that aggression must be cathartic - lacks validity, and therefore the entire hypothesis lacks face and concurrent (?) validity.