Complex sentence: McGroder was not yet interested in the upstart league and lobbying the NFL for an expansion franchise, and believed that the threat of the AFL would be enough to prompt the NFL to reconsider its opposition to expansion.
Split into simpler sentences: McGroder was not yet interested in the upstart league and was instead lobbying the NFL for an expansion franchise. He believed that the threat of the AFL would be enough to prompt the NFL to reconsider its opposition to expansion.