Wimbledon 2016: Serena Williams serve key v Angelique Kerber

Former Wimbledon champion Pat Cash takes an in-depth look at the powerful service game of Serena Williams, as she she prepares to defend her women's singles title against Angelique Kerber on Saturday.

WATCH LIVE: Wimbledon 2016: Women's Singles Final, BBC One, Saturday 9 July from 13:00 BST.

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