SIX MORE free kicks a game were paid under the AFL's trial of four field umpires, while an additional free kick was paid inside the 50m arcs.

Champion Data statistics reveal free kicks rose to an average 48 a game over the round 13 and 14 umpire trial, up from 42 under the existing three field umpire system over this year's first 12 rounds.

In the trial, an umpire was positioned inside each team's forward 50m zone, which resulted in 7.2 free kicks a game being paid inside the arcs, up from 6.2 in the opening 12 rounds.

The League's umpiring department will complete its review of the trial by mid to late this week.

Football operations manager Steve Hocking said earlier this month four field umpires could be introduced on a full-time basis in 2019 depending on the latest experiment's results.  

Four field umpires were trialed in AFL games late in the 2015 home and away season and over the next two seasons were used over the three bye rounds.

This year the umpires were used in a different structure than previous trials, in a move Hocking hoped would help extend the careers of the game's best officiators.

"In the past what we've tended to do is put that extra set of eyes around where all the numbers are," Hocking said earlier this month.

"(In this trial) there will actually be an officiating umpire within the forward 50 and the back 50 and there will be two central umpires as well.

"The other extension of that is we've got really, really good umpires, we've got some elite decision-makers, and as their age profile changes are we able to keep them in the game? Can they become umpires that are able to run less but retain their experience in the game?

"We're going to collect a lot of data on the back of this. All the umpires will have GPS (monitors) and (we'll) see if that lay-out, that structure, across the ground decreases their load as well.

"Does it also give us the ability to introduce younger umpires at either end of the ground? Potentially that might be one of the upsides to it and a bit of mentoring can go on with that."

Free kicks in 2018