Mr Ruck, 59, is currently in a critical but stable condition after suffering head and leg injuries.
The incident happened at 19:40 BST on Saturday on New Street, Kidwelly, Carmarthenshire.
A man from nearby Burry Port has been arrested on suspicion of causing serious injury by failing to stop at a road traffic collision, police said.
Mr Ruck is the author of four books and a columnist for local newspapers.
He had been walking when the incident happened and was taken to Swansea's Morriston Hospital for treatment.
Dyfed Powys Police has appealed for witnesses to the incident.

McGinn scored the opener as the holders beat Ayr United 3-1 in the last eight.
And the Scotland midfielder believes they have a squad capable of retaining the trophy and more importantly, sealing their return to the top flight.
"On our day, we're confident of taking on anyone," the 22-year-old told BBC Scotland after Saturday's victory over United at Easter Road.
Hibs advanced to join Rangers in the semi-finals, with Celtic and Aberdeen making up the last four after Sunday's matches.
The Championship leaders return to league duty on Friday night with a trip to third-place Dundee United.
And like his manager Neil Lennon, McGinn's main focus is on securing promotion to the Premiership.
"We're now only looking forward to Friday and whoever we get in the (Scottish Cup) draw, bring it on," he said.
"Our main priority this season is winning the league and we'll be doing everything we can to do that.
"We as club cannot afford another season in the Championship, it's really important we get out of it."
Like many Hibs fans, McGinn has been left perplexed by the Easter Road side's recent league form.
Scottish Cup wins against Ayr and Edinburgh rivals Hearts have kept their hopes of retaining that trophy alive, but Hibs have drawn three and lost one of their last four Championship matches.
"That's the frustrating thing for us," said McGinn, whose side are six points clear of second-place Falkirk and have a game in hand.
"But if we play like we did against Ayr then we can take on anyone.
"Everyone needs to be at the top of their game, we need to stand up and be counted, starting on Friday at Tannadice.
"Coming towards the end of the season, they're all going to be cup finals and we need to win all of them.
"If we do that, we'll be champions."
A 19-year-old man has been arrested over a suspected hit-and-run that left writer Julian Ruck seriously hurt.
[NEXT_CONCEPT]
John McGinn says Hibernian fear no-one after reaching the Scottish Cup semi-finals for the third successive year.