The officer, along with PC Archie Payne, 26, then attacked Scott Rooney when he protested about his friend Mr Smith’s treatment.
Wood, 26, was convicted of assault occasioning actual bodily harm and assault by beating. He will be sentenced at Westminster Magistrates' Court on Thursday, 3 June.
Payne, 27, was convicted of assault by beating. He was fined £600 and was ordered to pay £1,000 in costs in addition to a £34 victim surcharge.
Commander Paul Betts, from the Met’s Directorate of Professional Standards, said: “We recognise that officers face challenging situations on a daily basis and that the use of force is an unavoidable aspect of frontline policing.
“However it is essential that when force is used it is reasonable, proportionate and lawful. In this case, we felt that the force used by these officers was excessive and referred the matter to the IOPC.
“The criminal case has now concluded and a decision will be taken about what further misconduct proceedings should follow.”
In the footage, played at Hendon magistrates court during the police officers’ trial, Mr Smith is seen joining a melee close to Romford station before the alleged attack by PC Wood.
During the trial, prosecutor Nicola Shannon told the court that Wood struck Mr Smith's head.
“It looks as if there are likely to be four strikes, two of which appear to have connected with Jake Smith’s head", she said.
“PC Wood appears to go from the right to the left of the screen with his baton held above his head, and with an overarm motion he brings it down towards Mr Smith.
“At that stage, Mr Smith had his back towards him and was going away from the officer.”
When Mr Smith was later receiving paramedic treatment to his head wound, Mr Rooney remonstrated with the officers about their actions.
As he tried to take a picture of Wood’s shoulder number for an official complaint, he was pushed against a wall and then brought to the ground by Wood and Payne.
Payne later resigned from the Met in November 2020.