PHOENIX — The Democrat in the Maricopa County sheriff’s race filed a defamation lawsuit Thursday against incumbent Joe Arpaio over a TV ad that claims the challenger assaulted his ex-wife 13 years ago during an argument.

Democrat Paul Penzone denied the allegations made in the commercial that the Republican sheriff started running this week, saying his opponent ran the ad knowing the allegation was false.

“I have never at any time harmed my ex-wife or any woman in my life,” said Penzone, his eyes welling up as he expressed frustration over the commercial.

The Arpaio campaign said the ad was fair game. “This lawsuit is a political stunt,” Arpaio attorney Kory Langhofer said.

No charges were filed against Penzone in an argument that erupted in March 2003 as the couple was separated and sharing custody of their then-10-year-old son.

His then-estranged wife told police that Penzone had caused her to hit her forehead by pushing on a doorway, according to a police report.

Penzone told police that it was his wife who hit him in the head with a hockey stick during the dispute.

The dispute came as Penzone went to pick up hockey equipment for his son at her home.

The police report noted that Penzone suffered a minor bruise on his right cheek and his then-estranged wife had a minor bruise on her forehead.

City prosecutors in Glendale declined to prosecute either person because there were conflicting accounts without any independent witnesses and no reasonable likelihood of winning convictions.

Penzone and Langhofer refused to answer questions Thursday at back-to-back news conferences called by the campaigns. The six-term sheriff didn’t attend his campaign’s news conference.

Arpaio’s latest commercial said nothing happened to Penzone after the incident and the challenger isn’t the type of person who should be serving as sheriff.

Three months ago, a lawyer for Penzone sent Arpaio a letter warning him of the consequences of defamation.

The sheriff’s campaign also was given an affidavit written several months ago in which Penzone’s ex-wife said she can’t let Arpaio’s “dishonest representation” repeat itself.

The challenger said in a campaign video earlier this week that Arpaio apologized to him late last year for running a 2012 ad, but he said the sheriff has since changed course.

Penzone was working as a sergeant for the Phoenix Police Department at the time of the dispute. He has since retired and remarried.

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