Robert attempts to avoid paying Andrew a commission on the sale of his house to a buyer procured by Andrew. He does so by waiting until after the listing agreement has expired. Andrew finds out about this after Robert sells his house. Andrew can:

sue Robert for breach of contract

Explanation: Robert could be sued by Andrew for breach of contract which is the violation of the legal terms of an agreement between two or more parties. Breach of contract occurs when one or more of the contracting parties fail to honor the one or more of the terms stated in the contract term.

In the scenario above, Robert trying to dodge the commission which should be paid to Andrew is an act of violation of the contractual terms of their agreement, and he certainly Robert could be sued Andrew for breach of contract.