New first-team coach & "defensive co-ordinator"

[Injury Time]

Almost missed this buried in another "prospect gone crock" article but had seen him a couple times in reserves...

Former Arsenal defender Ryan Garry has been forced to retire from football at the age of 27.The versatile full-back, who featured in Arsenal's 2001 FA Youth Cup Final triumph, has called time on his playing career at Bournemouth after failing to recover from a persistent nerve-related problem in his lower leg and will become first-team coach and defensive co-ordinator at the club.A former scholar at Highbury, Garry signed professional terms with Arsenal in July 2001 and made his first-team debut in Arsenal's 3-2 Worthington Cup Third-Round defeat at home to Sunderland in November 2002.His only Premiership appearance was in a 6-1 victory over Southampton in May 2003, the game that started Arsenal’s 49-game unbeaten run.

Okay football gurus what is a "defensive co-ordinator"?