The incident happened on Marshalls Cross Road at around 7.30pm when emergency services responded to reports of an altercation on the grass verge by the roadway.
A 17-year-old boy was treated by ambulance staff and has since been taken to hospital where his condition is described as serious but not life threatening.
T/Superintendent Paddy Kelly said: "Although this incident did not happen at the fireworks display, it is still shocking which again, although is believed to be targeted, has taken place in an area where there are undoubtedly lots of innocent children and members of the public wondering around.
"This is currently a live investigation and officers at the scene are working with security staff to secure the area, analyse CCTV and conduct forensic analysis and urge anyone with information to come forward quoting log 1051 of 5th November. We cannot have this sort of reckless and brutal behaviour and we will do everything we can to bring the offenders to justice."
Please call 101, DM @MerPolCC or @CrimestoppersUK with any information.