Teenager charged with assault after man seriously injured in alleged rock-throwing attack in Falcon

A 14-year-old boy has been charged with assault after a man was seriously injured and left convulsing on the ground in an alleged rock throwing attack in a fast food restaurant car park.

Police say an altercation took place on Monday afternoon between a group of juveniles and a 25-year-old man outside a Hungry Jacks in the Mandurah suburb of Falcon, south of Perth.

During the incident, the man allegedly had rocks thrown at him, before the 14-year-old allegedly threw a rock that caused him to fall face first on the bitumen, leaving him unconscious.

Police said the man and the group of children did not know each other.

The incident was filmed and posted on social media, with at least six juveniles seen crowding around the man in a car park with some filming on their phones.

The ABC has blurred the identities of the people in the video for legal reasons.

Mandurah acting senior sergeant Jamie Raper said the footage was very confronting.

"It's very horrific ... and obviously we can understand why the community is quite upset about that," Sgt Raper said.

"We believe there might have been an altercation earlier in the restaurant where the juveniles were potentially harassing the workers there and we believe this male has stepped in to protect those workers.

"We don't encourage people to step into these incidents … we don't want members of the community hurt, we'd prefer if they do step back and call Triple Zero."

The 25-year-old man was taken to Peel Health Campus with severe facial injuries and has since been released.

Sgt Raper said he will require ongoing medical treatment with a long road to recovery ahead.

Police have since arrested and charged a 14-year-old boy with assault occasioning bodily harm and he will appear in court later this month.

Sgt Raper said police knew the identities of others in the group, and were investigating further.