David Frost, a former minor hockey coach and National Hockey League agent, pleaded not guilty Tuesday to four charges of sexual exploitation.

Frost, 41, entered the plea at the start of his trial in Napanee, Ont. He is being tried over alleged incidents involving 15- to 17-year-old boys and girls in 1996 and 1997, when he was coaching the Quinte Hawks junior hockey team.

At the time, Frost lived in a motel in Deseronto, a town of about 1,800 located 200 kilometres east of Toronto, where the Hawks were based.

A court order bars publication of the names of the alleged victims.

Lawyers for the Crown and the defence spent much of Tuesday arguing about whether certain witnesses should be allowed.

The Crown wants to hear from three former Quinte Hawks players, who are expected to testify that Frost was a tough, demanding coach who abused his power over some of the players. The defence has argued that they have no relevance to the case.

"There is no question that he was a tough coach, a demanding coach, an aggressive coach," Frost's lawyer Marie Henein said.

She argued it would amount to an "extraordinary, wild-goose chase" to listen to a host of witnesses who are prepared to portray Frost as a sometimes violent, angry and controlling man who belittled and abused the teenage boys he coached.

"It has no link to the incidents whatsoever," Henein said.

She urged Justice Geoff Griffin to refuse to consider the evidence that prosecutors want to introduce about Frost's coaching.

Crown lawyer Melanie Adams said prosecutors should be permitted to call witnesses to Frost's coaching tactics because the incidents demonstrate the degree of control he exerted and the authority he had over his teenage charges.

"He always told them that he had the ability and the authority to send them home and end their hockey careers," Adams said.

When prosecutors charged Frost, court documents listed 119 people as potential witnesses.

Arguments about the admissibility of evidence took up most of the opening day of the trial.

A broad court order imposed in 2006 when Frost was charged also prevents publication of the names of people who may appear as witnesses.

Frost was arrested in August 2006 after a two-year investigation by the Ontario Provincial Police and initially charged with 12 counts of sexual exploitation and one count of assault.

All but four of the charges were later dropped by prosecutors due to insufficient evidence.

In a separate case, Frost is set to go to trial in April 2009 on fraud charges over the alleged use of a credit card belonging to Mike Danton, a former St. Louis Blues hockey player now serving time in a U.S. federal prison for plotting to have Frost killed.

Frost was Danton's coach and later his agent. Their relationship led to the player becoming estranged from his family.

Despite pleading guilty in November 2004 to plotting Frost's murder and receiving a 7½ year sentence, Danton, a Brampton, Ont., native has continued to defend Frost.

Frost resigned as an NHL agent in December 2005 and has denied he was the intended target of the murder-for-hire plot.

Before becoming a player agent, Frost spent several years coaching minor and junior hockey.