Definition from Wiktionary, the free dictionary
- (intransitive, baseball) To throw a pitch at a much slower than expected speed.
- He changed up on Wilson after three fastballs and struck him out.
- (intransitive) To confuse someone by doing something unexpected or in an unexpected way.
- I thought that we were going to study the project some more, but then he came back from the weekend and changed up, making it a top priority.