Actually the Jets made TWO roster moves today:
Igwebuike was always a possibility for a waiver claim because he came from the Philadelphia Eagles, so Joe Douglas will be familiar with him. The Eagles claimed Igwebuike about six weeks before Douglas left to take the Jets' general manager job.
Igwebuike saw action with two teams (the Bucs and 49ers) as an undrafted rookie last year. In all, he had two tackles in six games, playing exclusively on special teams. In preseason, he had 13 tackles and a pass defensed.
Clark, a former Mike Maccagnan draft pick, was coming of an ACL tear when the Jets drafted him and his progress has constantly been set back since then by further injuries. He played just two games as a Jet.