Question

fix any errors with subject - verb agreement below. click submit answer if there are none.
tony stark, not his father, fit into his grandfathers old baseball glove.

Explanation:

The subject of the sentence is "Tony Stark", a singular third-person noun. The verb must agree with this singular subject, so "fit" is corrected to "fits". The phrase "not his father" is an interrupting phrase that does not change the number of the main subject.

Answer:

Tony Stark, not his father, fits into his grandfather's old baseball glove.