Ramani Sanderson, aged 20, is accused of murdering 21-year-old Shane Mayer outside Gabba's Bar in Darlaston on the night of July 24, 2019, which he denies.
In a separate incident, Sanderson, of Walsham Road, near Peckham, London, is also charged with wounding a taxi driver near Bradford Arms pub in Walsall, on April 29, 2019. He also denies this.
However, before Sanderson began giving evidence at Birmingham Crown Court on Tuesday, he pleaded guilty to possessing a knife in relation to both of those incidents.
A further three defendants are also charged with murdering Mr Mayer, who lived in Wolverhampton, and possessing a pointed article in a public place.
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The judge presiding over the case, Simon Drew QC, asked jurors not to let Sanderson's guilty pleas sway their judgement regarding the other defendants.
Mr Drew told the court: "The two counts that were put to him [Sanderson] were counts two and four. They were counts of possessing a bladed article and he has pleaded guilty to each of the counts.
"The other three defendants face similar counts to count four. You must not hold his guilty pleas against them on either count. In relation to count four, you still need to reach verdicts in relation to each of them."
The other defendants are Lewis Green, 21, of Heathfield Lane West, Darlaston; Joseph Till, 21, of Summer Street, Willenhall, and Kamron Reid, 20, of Herberts Park Road, Bloxwich.
They deny murdering Mr Mayer, and possessing a bladed article. Green admits carrying a hammer.
Sanderson began his evidence with questions from his defence counsel, Michael Duck QC, where he spoke about his background and then the taxi incident.
Sanderson said he began carrying knives between August and December 2018 following a "fist fight" he had in Wednesbury, the court heard.
He said this incident caused him problems at later dates, where he was threatened with knives on two separate occasions, and he started arming himself for self defence.
On the day he allegedly attacked the taxi driver in Walsall, Sanderson took out with him a knife, loaned from a "friend of friend", because he was previously threatened with knives in that area, the court heard.
He and four other people were picked up by the taxi driver, who became "super upset" when they got in and the driver started swearing, said Sanderson. He then physically assaulted the driver, the court heard.
Initially, Sanderson struck the driver three or four times, which he accepts doing, before throwing the man's phone across the road to be a "nuisance".
He then allegedly struck the driver on the head with a knife. He was subsequently charged with wounding with intent, which he denies.
Mr Duck asked him: "Were you intent on seriously injuring him or not?" Sanderson replied: "No."
Mr Duck added: "What was your intention when delivering that blow?" Sanderson replied: "It was a warning".
The trial continues.