Complex sentence: After having joined Mexico's Tigres de la UANL in 2007, Abreu was able to rescind his contract with them in order to join Club Atlético River Plate--the Mexican Football Federation stalled on recognizing the transfer because of an imposed moratorium between the sides.
Split into simpler sentences: After having joined Mexico's UANL Tigres in 2007, he was able to rescind his contract with them in order to join Club Atlético River Plate. The Mexican Football Federation stalled on recognizing the transfer because of an imposed moratorium between the sides.