A 16-year-old boy was taken to hospital after a "fight" in broad daylight in Willesden.
The teenager suffered a blow to the head after the assault in High Road, on Tuesday (July 4).
Emergency services rushed to the scene at around 5pm, where passers-by looked on as medics treated the teen.
Police confirmed they were called to "reports of people fighting".
A Metropolitan Police spokesman said: "A 16-year-old-youth was found with a head injury after apparently being struck on the head.
"He was taken by London Ambulance Service to a central London hospital, where his injuries were not found to be life changing or threatening.
"Four men aged 18, 20, 21 and 21 were arrested in connection with the assault."
Police enquiries are ongoing.
Keep up to date with the latest news in west London via the free getwestlondon app.
You can set up your app to see all the latest news and events from your area, plus receive push notifications for breaking news.
Available to download from the App Store or Google Play for Android .
