The demonstrators have been making headlines over the last few weeks for protesting what they see as the gentrification of the low-income neighbourhood.
Const. Brian Montague says the victim and the other protesters have been uncooperative, so a motive for the attack is unclear.
"They wouldn't supply their names, they wouldn't supply a statement as to what happened... so we're left with a point here where we don't have a lot to work with."
Police will be asking local businesses if they have security video that may provide some clues.