He represented New Zealand from 2004 to 2010, making his debut at the 2004 Olympic Games.
Giving evidence, Mr Johnson said he was working as a doorman at The Bunker Bar early on the morning of June 13, 2014, when Bradshaw and two other men approached him.
When he refused the trio entry on the grounds one of the men was highly intoxicated, they set upon him.
As Bradshaw held him by the scruff of his neck, he was punched repeatedly by all three, and eventually fell to the pavement under their weight, he said.
As he went to get to his feet, Bradshaw kicked him in the head "like a conversion'' kick in rugby, and was he punched several more times.
It was his worst attack in his eight years as a bouncer, prompting him to quit the profession the next day.
Under cross-examination by defence counsel Liam Collins, Mr Johnson was asked why he told a police constable soon after the incident that he "thought'' Bradshaw had kicked him.
Mr Johnston said he was dazed at the time, and was now "100% sure'' that Bradshaw had kicked him.
An off-duty bouncer who witnessed the attack, Julian Joel, told the court he tried to defuse the situation by standing between Mr Johnson and his attackers, but backed off and called the police when it continued to escalate.
A few hours earlier, he had asked the trio to leave the strip club where he worked, The Club, after one of the defendant's companions abused a female staff member.
Under cross-examination by Mr Collins, he said he did not see the defendant kick Mr Johnson.
Giving evidence, Bradshaw said an ankle reconstruction operation in 2012 had ended his basketball career and left him with a permanent limp.
Running and kicking Mr Johnson in the way described was therefore "physically impossible''.
Bradshaw said Mr Johnson had put one of his companions in a chokehold after he jumped over a barrier, and the situation escalated only because he refused to release him for two or three minutes.
"We were the ones who were the victims, in a way.''
He also denied punching and verbally taunting Mr Johnson, but admitted to holding him by the scruff of the neck to try to make him release the chokehold.
Under cross examination by prosecutor Sergeant Ian Collin, Bradshaw admitted his group had been kicked out of two bars earlier in the night and refused entry to a third.
His two companions on the night were granted police diversion.