It is not strictly necessary for pokemon battles to have referees determine when a pokemon is knocked out. Pickup matches, practice games, and even some low-level tournaments around the world include only two competitors and their respective teams, with winners disputed only in extremely rare situations – most commonly in the event of a double knockout. The other major exception is when a Morgrem is one of the competitors, for it was in the aftermath of bitter disputes about this notoriously sneaky pokemon that the Galar League began using referees in the first place; indeed, official regulations at low-level tournaments require a referee to be chosen from the crowd or other contestants whenever a Morgrem, Grimmsnarl (which inherits its prevolution's techniques), or Gliscor (which is also known for trickery, if less effectively) participates.
The question of when a battle has concluded is older than the concept of Pokemon battles as sports; indeed, some scientists have even theorized that Morgrem evolved to exploit precisely that ambiguity. Admittedly, the quick-fire spears on its head (or "hair", as it is often inaccurately described by those lacking familiarity with this pokemon) are suggestive of this possibility, but it is difficult to imagine how wild pokemon could be repeatedly fooled by these gestures of supplication. More recently, Galar's famous royal family, which originated in Coumarine city, first gained the throne when the ducal Morgrem used a feigned surrender to assassinate the last of the original kings, granting its trainer both the throne and a massive headache trying to justify what it had done.
Modern rules view Morgrem's false surrender as a legal maneuver, and trainers must be advised that no pokemon is officially knocked out until the whistle blows; referees must also be quick on their feet, so as to avoid serious injury to defeated pokemon.