Sebastian Jones said he had punched victim Reece Cox, aged 24, after Mr Cox had punched his friend Shaquel Halliday, a judge heard.
The 19-year-old defendant, who denies murder and other charges, told a jury he didn’t want Halliday, who is also on trial, to “get hit again”.
Mr Cox died outside The Clifton pub on Bull Ring, on August 15 last year after he attempted to break up a fight.
Six men, including Jones and Halliday, deny murder.
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Jones, who was 18 at the time of the offence, had been out with a group to celebrate Halliday’s birthday with a group of people, Wolverhampton Crown Court heard.
They had been to three pubs before they headed to The Clifton pub at around 11pm, before a fight broke out between one of Jones’ friends and Grant Danbury, jurors heard.
Jones told Wolverhampton Crown Court he had tried to restrain his friend but was unable to, and he had swung out at Mr Danbury who then fled toward The Clifton pub.
The 19-year-old said he had met up and walked with Halliday to where Mr Cox was being confronted to see “what was going on” and told jurors Mr Cox had looked “very aggressive”.
He told the court: “I didn’t know this man and all I saw was that he’s bigger than me, being aggressive and telling people to ‘come on’ and that was intimidating.”
Jones said he had witnessed Mr Cox punch Halliday and he “immediately went over” to punch Mr Cox in order to protect his friend and ensure he didn’t “get hit again”, a judge heard.
The defendant admitted to punching Mr Cox a number of times in the back and claimed he had been pulled into an alcove by Halliday, away from the incident, which the prosecution disputed – claiming it was the momentum caused by the victim falling, a court heard.
Jones said: “I remember getting pulled back into the alcove. I thought I was going to be attacked. It looked like he [Mr Cox] was getting up off the floor, he was on his knees going to get up.
“I picked myself up off the floor and I swung my leg out and I kicked him and got out of the situation. I felt very vulnerable in the doorway. I think I kicked him in his neck and head area, [but] I didn’t aim for his head.”
Adam Ashwin, 20, of Monument Lane, Sedgley, denies murder.
Wayne Burke, 23, of Queens Street, Pensnett; Shaquel Halliday, 22, of Shadwell Drive, Lower Gornal; Shane Jones, 26, of Orchard Grove, Lower Gornal; Ryan Nicklin, 22, of Limes Avenue, Pensnett; and Sebastian Jones, 19, of Corser Street, Dudley, deny murder, manslaughter, assault actioning actual bodily harm and violent disorder.