Sentence:  "You sure did [hit someone with the snowball]," added Teeter, stiffling a laugh. "And of all persons in the school but Professor Rodd. Oh my! Oh wow! You're <WSD>in for it</WSD> now! He won't do a thing to you fellows! Look at his hat! Here he comes!" 
Meaning of the word marked with <WSD> tags:  In trouble.