Following a minor traffic incident, the teenager confronted a 67-year-old man and without provocation punched the man to the head once and knocked him out.
"He is appearing today in the North Shore District Court charged with Assault with Intent to Injure," police said.
In both instances, police tracked down the attackers and they wanted to thank the members of the public who assisted them in their investigations.
They said several public members stopped on both occasions and assisted with medical assistance to both victims. Dash camera footage was also supplied.