A court has heard a former NSW Northern Beaches baseball coach allegedly kept torture tallies, diaries naming his child victims, footage of alleged assaults and was in possession of child pornography.

Stuart Mould is facing 19 charges including 16 counts of common assault, one count of assault occasioning actual bodily harm, producing child abuse material and producing child pornography.

The 70-year-old was arrested at his Sanctuary Point home on the South Coast yesterday and appeared in Nowra local court today.

The alleged historic assaults span from between the 1994 and mid-2017 while he was a baseball coach at the Pittwater Sports Club.

Police say five men reported being physically abused while they attended the sports club as children.

They were between nine and 20 years old at the time of the alleged assaults, with one alleged assault so severe it resulted in the foot of a 12-year-old boy being fractured.

Diaries found

Mr Mould sat in the dock quietly as a police prosecutor told the court they had found diaries naming further victims, along with video footage of assaults and a torture tally of his victims during the execution of a search warrant at his home.

Police allege Mr Mould would film the assaults.

Police will allege Mr Mould had specific names for punishments which would be administered if the boys made a mistake, including toers, crushers, twisters and lazos.

Court documents show a toer involved pulling a child's foot to his groin and twisting the toes outward in a prolonged and aggressive manner to cause pain.

They also allege twisters involved the boys taking off their shirts, for Mould to twist their nipples."

Refused bail

The prosecutor also alleged police had found evidence on Mr Mould's phone that he had been actively messaging young people in the community, however it was too early in the investigation to lay further charges and did not elaborate on what the nature of those messages were.

Mr Mould did apply for strict bail, however the magistrate said he had concerns about Mr Mould fleeing given the strong case against him.

He was refused bail and will reappear in a Sydney court next week.