Usually those that show emotion also will get labeled by others as trying to intimidate or taunt their competition. I am sure there is some truth to that.
Example: I have been to high school bowling events, there are teams that don't shut up until the match is over. Constantly encouraging and going nuts when ever someone strikes or picks up a spare on their team in the match. You will hear parents on opposing teams (that do not do those things), stating how disrespectful it is and should not be allowed.
Is there a line? Can a team/person go overboard with this and be considered poor sportsmanship?
I think showing emotion at an event is a good thing. I am not sure what the line should be. I seen plenty of teams get really loud, especially with parents adding to the noise. Maybe because I have seen it enough times, it doesn't bother me.
Being to enough of these things, I know one thing: Loud and excitement doesn't always equal to winning or in the lead.