Mr Richards volunteered as the tail walker for the free timed 5k run, which takes place on the Stray every week.
Mr Richards took part with staff and pupils from St John Fisher Catholic High School to support the campaign to raise the Â£75,000 needed to fund a life-changing prosthetic leg for Year 13 student Jordan Teodori-Faith, who has Proteus Syndrome.
He said he was delighted with the response he got from the staff and pupils.
On completing his 100th event, he said: "parkrun is such a fantastic concept. It is for everybody, whatever their shape or size, and it's free - everybody is a volunteer.
"There is a real camaraderie about it that makes everyone so supportive of each other."