Complex sentence: In the 2011--12 season, Alderweireld made significant strides in his ability as a footballer, also forming a formidable partnership in the heart of the Ajax defensive with captain and fellow Belgian Jan Verthongen.
Split into simpler sentences: In the 2011--12 season Alderweireld made significant strides in his ability as a footballer. He also formed a formidable partnership in the heart of the Ajax defensive with captain and fellow Belgian Jan Verthongen.