To crumple something into a small lump or ball (i.e., a "wad"). A noun or pronoun can be used between "wad" and "up." My heart sank when I saw him wad the note up and toss it on the ground.Don't just wad up your papers and stuff them in your bag—put them in a folder or something, for crying out loud!
wad up
v.
To crumple or compress something into a wad: I wadded up the piece of paper and threw it in the trash. The janitor wadded the tissues up and threw them away.