...the new freshman that just wanna mess around...
ah, let me just start by saying everyone has one or more of those incoming freshmen in their band, nothing out of the ordinary though, its normal.
A)Let them know what's up. Tell them that the shouldn't be doing what they're doing and make sure to state why it is wrong(either in front of your section or on a one on one) But be careful of it is a one on one conversation that it is not a scolding; or else he/she won't listen and you'll be wasting both of your guys' time. Make sure its a serious but a not too
B) If it gets to be where you can't do anything more, let your drum major have a talk with him/her.. maybe they'll listen to an important leader in the band.
C) But it it really does get out of hand, let your director know asap.
hope this helps . . .