It is possible, but it is slightly more involved then calling a single method.
In order to accomplish this, you'll need to loop through all the players in the game and check to see what value their property TeamColor holds. If it is the same as the color of the Team you are counting, then you increment a counter variable by 1. Once you have gone through all of the players, the counter variable will be equal to the number of players on the team.
####Example:
local function countTeamPlayers(teamColor)
local numPlayers = 0
for _, player in next, game.Players:GetPlayers() do
if player.TeamColor == teamColor then
numPlayers = numPlayers + 1
end
end
return numPlayers
end