Andrew Young, 40, died after being struck in the unprovoked attack by Lewis Gill, 20, in Bournemouth, Dorset, on November 6 last year.
A chilling video of the assault was released by police.
Andrew's mother spoke of her outrage after Gill was given a four-and-a-half-year jail sentence for the punch that killed her son.
“I saw the CCTV footage in court and you can see that Andrew didn’t cause Lewis Gill any harm," said Pamela Young, 71. "The sentence is an absolute joke."
More top news
The chief executive of one of the 'big six' energy companies tells ITV News a report customers are paying too much is a concern.
10 years on, George Psaradakis has given his first interview, recalling the events of July 7 2005.
A spat between the supporters of Yvette Cooper and Liz has seen a debate rage over whether a woman needs to be a mother to be a good leader.