Complex sentence: Boldin refused the pay cut and was expected to become an unrestricted free agent at the start of the NFL year on March 12,2013 until he was traded to the San Francisco 49ers.
Split into simpler sentences: Boldin refused the pay cut and was expected to become an unrestricted free agent at the start of the NFL year. So, on March 12,2013 until he was traded to the San Francisco 49ers.