An off-duty nurse, who was kicked to the ground by a gang of drunken teenagers in a Wigan park, was saved from more serious injuries by her dog.
A teenage girl from the gang of four punched the 30-year-old as she walked her retriever in Haigh Country Park, said police.
A second girl and two boys, who had all been drinking, joined in and dislocated her arm and kicked her repeatedly.
The dog, called Bailey, bit one of the girls and chased the gang away.
'Peace of mind'
Det Con Kevin Telford said: "This was a motiveless and senseless attack on a nurse, probably fuelled by alcohol, that could have been worse had Bailey not came to her owner's aid.
"This sort of attack is thankfully rare, but it does not lessen what this woman has been through and how important it is we find those responsible."
He appealed to the public and to medical staff for help in tracing the attackers.
"At least one of the girls suffered bites to either her leg or face and had her clothing ripped, so I want to ask any parents living in the community, 'Have you found your daughter's clothing in a mess or discovered any bite marks?'.
"If you have then please do the right thing and call us because this woman deserves the peace of mind of knowing who is responsible.
"I would also appeal to any nurses or doctors who might have treated a young girl for bite marks to call us."
The victim suffered a dislocated left shoulder, two black eyes, cuts around both eyes, swelling and bruising.
The attack, on 4 November at 1130 GMT, happened close to the Wigan Lane entrance of the park.