The incident happened in broad daylight on May 16 when a brawl broke out in Clement Street in Accrington at around 8.20am.
A police spokesman said: "It was reported that a man was trying to attack a second man with a hammer, who responded by throwing a wheelie bin at his assailant.
"A third man then got involved in the fight, removing the seat post from his bike and hitting the first man a number of times and kicking him while he was on the floor.
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"The second man then wrestled the hammer from the first and hit him with it."
A 35-year-old man from Blackburn and a 41-year-old man from Accrington were arrested on suspicion of Section 18 assault.
Both have since been released under investigation pending further enquiries.
Detectives have today (Wednesday, July 5) released CCTV pictures of a third unidentified man who they want to speak to.
"This was a shocking incident which happened in broad daylight," said DC Ruth Stott, of East CID.
"Although we appreciate it will have caused concern in the community, this is very much being treated as an isolated incident.
"We have made significant progress with this investigation and have already made arrests.
"Our enquiries are very much ongoing to identify everyone involved and we now want to speak to the man in the CCTV.
"If you recognise him or have information on his whereabouts, I would urge you not to approach him but to contact police as soon as possible.
"I would also like to appeal to the man directly, if he sees this appeal, to get in contact with police."
Anyone with information is asked to email [email protected] or call 101, quoting log 0325 of May 16, 2021.