Gladstone is standing trial with Cooper but on an allegation of recklessly discharging a firearm.
The pair's trial is expected to take at least two weeks.
The names of 24 Crown witnesses were read to the court, resulting in several potential jurors asking presiding judge Robert Dobson to excuse them due to connections with the case.
Opening for the Crown, prosecutor Rebecca Guthrie said it was Gladstone's actions at an annual horse sports event in Hicks Bay two days earlier that triggered the entire incident.
As was typical in cases arising out of small communities, there were familial links between Gladstone and Tauhore their partners Mary-Jane Waitoa and Noleen Brooking were cousins with a close relationship.
The two women were together at the horse sports when Ms Waitoa prepared to leave.
Worried that her partner Gladstone had been drinking alcohol all day and might drive and crash her car, Ms Waitoa tried to get the keys from him.
But he refused to hand them over. Ms Brooking also asked him but he also refused her efforts and, heavily intoxicated, he challenged her to "scrap", she said in evidence.
Her response was that he should know it wouldn't be her he would have to fight (meaning it would be her partner, Mr Tauhore).
Ms Brooking said she walked away and did not tell Mr Tauhore about Gladstone's remarks until later.
While angry with Gladstone, Mr Tauhore ultimately decided to let the matter go, Ms Brooking said.
The next day, he learned his uncle in Wellington had died and the family wanted a tangi at Te Araroa.
Mr Tauhore called on fellow gang members, all 12 of whom lived in Gisborne, to come up the Coast to help prepare the local marae. Six or seven of the men arrived and were helping when Mr Tauhore got further word that the tangi would be held elsewhere.
Ms Brooking said the men redirected their efforts to gravelling her driveway and at the end of a hard day's work, Mr Tauhore took their 4-year-old daughter and the gang members (who followed in two vehicles) for a swim at Hicks Bay.
They could have swum closer to home but Mr Tauhore wanted to show his friends his favourite swimming hole in the river, she said.
Ms Guthrie said it was on their way back from that swim that Mr Tauhore stopped with the group outside Cooper's home. He was shot as he advanced over a field in front of the house.
The bolt-action rifle used by Cooper was taken there a short time earlier by Conrad Rickard. Cooper, Rickard and Gladstone had gathered at Cooper's house in anticipation of Mr Tauhore going there because of Gladstone's comments at the horse sports.
Outlining the defence position, Mr Fairbrother said sometimes people were put in such extreme situations that they had to protect themselves.
There were children and adults at the property when "this man" (Mr Tauhore) came, wearing his Black Power regalia, Mr Fairbrother said.
He wasn't stopping he went straight through a ditch.
Alluding to a mistake Cooper made at the start of the trial by responding "guilty" when the charge was formally put to him, Mr Fairbrother said jurors could see for themselves that Cooper was not a sophisticated man.
The defendant admitted firing the shot but in law he was entitled to take whatever steps appeared reasonable as he saw events unfolding. Cooper was frightened. There were mortal threats being made.
He knew Mr Tauhore's reputation as "a killer", Mr Fairbrother said.
Cross-examining witness Charlie Ngatai-Brown, Mr Fairbrother had him confirm that Cooper was a decent, family-oriented man who led a sober life and trained horses. He was not someone who would normally be associated with guns.
Cooper had turned down a request by Mr Tauhore to join his gang.
For Gladstone, lawyer Tiana Epati said that similarly, her client did not dispute discharging the .22 rifle but used it in the most minimal way. He did not fire directly at anyone and fired only to warn off Mr Tauhore and the gang group.
She had one of the Crown witnesses, Teohomauri Piripi Bartlett, confirm that Mr Tauhore had gone looking for Gladstone at a party after the horse sports. Mr Tauhore spoke of dragging Gladstone, who had passed out at a table, from the property but others persuaded him to leave.
