AFL umpires coach Hayden Kennedy is confident the league will ultimately adopt a four-umpire system, but has guaranteed there will be no change to the current officiating model this season.

The AFL will increase the number of field umpires from three to four in eight NAB Challenge matches this year to try to determine if an extra official can bring down error rates.

Kennedy, who officiated in five grand finals, said the league had conducted extensive studies of US sports, in particular American football, before deciding to go ahead with the trial.

“In a nutshell, I think it could be the way to go,” Kennedy said on Wednesday.

“The whole philosophy around it is about just getting a different angle to what we’ve (already) got. With three umpires we’re trying different angles, but we know that we’re not covering them all – four umpires could provide us with that extra angle.

“We know that we make errors. The whole idea of the four-umpire system would be to try and reduce the amount of errors that we make – that’s all it is.”

Four umpires have already been trialled in intra-club games at Carlton and Collingwood last week, with Kennedy reporting positive early feedback.

The extra umpire will predominantly be used to officiate the space between the play and the boundary line.

While Kennedy is optimistic the trial will prove a success, he admitted there could, initially at least, be some issues associated with having an extra official on the ground.

“There could possibly be, but that’s why we need the vision and we need coaching, if it comes in, to make sure that we try to eliminate (that),” he said.

“When we went from two to three (umpires) I remember the same conversations, so I’d be pretty confident that it could work out.”

Kennedy has been touring the country with AFL umpiring director Wayne Campbell presenting two new rule interpretations to clubs ahead of the season.

Umpires will crack down on the players with prior opportunity in holding the ball decisions this season and will also seek to better police blocking in two-on-one marking situations.

“With the prior opportunity I’d be confident in saying that there’s 100 per cent acceptance (from the clubs) – they really understand what’s going on,” Kennedy said.

“With the blocking and marking there was a little bit of an issue (initially) … but once we went through and explained it I think it’s been pretty well accepted.”