Murdered teenager Stephen Lawrence was innocently chatting about football with his friend moments before he was stabbed in the street, a court has heard.
Hospital worker Royston Westbrook told the Old Bailey that he saw a group of white men "collide" with Mr Lawrence and Duwayne Brooks and violently attack them.
Mr Westbrook re-lived the events of the night that Mr Lawrence died in Eltham, south-east London, in April 1993.
Gary Dobson, 36, and David Norris, 35, both of south London, are on trial for the murder, which they deny.
Mr Westbrook told the court: "The two black boys, Stephen and Duwayne, were standing right by the bus stop. They were kicking about, they were talking about football... they were just generally chit-chatting."
The teenagers were discussing whether or not they should wait for a bus or walk back up to a roundabout to try to get another. In the end they made the fateful decision to walk away, and were set upon by the gang.
Mr Westbrook told the court: "They just collided - that's what it looked like. They were just heading towards each other and that was it."
Re-living the attack, which happened more than 18 years ago, he went on: "They grabbed Duwayne Brooks' wrist but he turned his wrist and just pulled away. Duwayne ran towards the bus stop where we were standing and turned round and shouted something like 'Leg it, Steve' or 'Run, Stephen'."
Mr Brooks managed to run away but Mr Lawrence was forced to the ground. Mr Westbrook told the jury: "I saw them surround Stephen and he went down basically through sheer weight of numbers in the middle of them... it looked at the time that someone went to punch him. It was so quick, it really was quick - it was about 10 seconds - and my impression going away from that was that they managed to punch him and that was it."
Moments later, while on a bus, he saw the stricken teenager lying on the ground.