David James Reginald Davies, 44, of Carrington Road, Adlington, Chorley, admits causing motorist Lewis Flynn actual bodily harm.
Sarah Magill, defending, said it appeared the pair had been goading each other in the lead up to the incident.
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The court was told Mr Flynn was travelling far too close to his vehicle and ploughed into the back, and the assault then took place.
Miss Magill said: “He says he just lost his temper completely and very much regrets it.”
The Honorary Recorder of Preston, Judge Mark Brown, ordered a pre sentence report on Davies, who has no previous convictions.
His sentence will now take place on February 21, and he was given unconditional bail.