If you are 21 years or older and you purchase or provide alcohol to anyone under 21, you can be charged with Unlawful Transactions with Minors, which is a misdemeanor punishable by up to a $1,000 fine and 6 months in jail. Even worse, if anything bad happens as a result of that transaction, you could be held liable.
MSU's Student Legal Services program is managed by the Associated Students of Montana State University (ASMSU). Please thank your student government for prioritizing legal services for MSU students!