The incident happened in Old Mill Road at around 3.35pm on Wednesday, March 15.
There was a physical altercation between four men, in which two of the men suffered significant injuries and were taken off in Ambulances.
A female driver posted on facebook saying "I drove past and saw a man with a bloody face"
At just after 3pm the Old Mill road was closed off. Just up from the Shell Petrol Station on Watford Road near to the M25 junction 19 / 20.
DC Nick Surridge, from the Three Rivers Local Crime Unit, said: “This incident happened on a busy road during the daytime so I am confident there would have been a lot of people around. If you witnessed the assault, even leading up to or just after it, then please come forward and speak to us if you have not done so already. Any information you have could be crucial to our investigation.”
Hertfordshire Police were still at the scene into the late evening as forensics continued the investigation.
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