Career
Born in Slough, Clifford came through the Chelsea academy, having signed with them at the age of 8. He turned professional in 2010. He played in Chelsea"s pre-season friendly away to Ajax, and on 18 October he joined the first team for an away Champions League game against Spartak Moscow, where he was an unused substitute.
Clifford signed a new four-year contract for Chelsea in September 2011.
On 19 March 2012, Clifford made headlines when he, along with Jacob Mellis, setting off a smoke grenade and causing a full-scale evacuation at the club"s Cobham training ground. The pair escaped with a fine after admitting he brought the grenade – understood to be from a paintball expedition – into Chelsea"s Cobham training headquarters.
The pair were suspended after the incident on 2 March, though Mellis was sacked. On 11 January 2013, he joined Colchester United on a one-month loan deal, before making his debut for the U"s the very next day as they fell to a 2–1 home defeat to Scunthorpe.
A club-record ninth successive defeat.
Having been joined in Essex by his Chelsea team mate Sam Walker, also on loan, Billy started the remaining four games of his initial loan spell as the U"s fortunes began to turn. He made his final appearance for the club on the final day of the 2012-2013 season, helping the club secure a 2–0 away victory at Carlisle United to guarantee League One safety. On 10 July 2013, Clifford joined Football League Championship side Yeovil Town on a six-month loan deal.
He made his debut for Yeovil as in their Football League Cup first round victory over Southend United, on 6 August 2013.
On 25 August 2013, Clifford returned to Chelsea after failing to break into the Yeovil first team On 30 January 2014, Clifford was loaned for the rest of the season to Belgian club Royal Antwerp, then managed by former Chelsea striker Jimmy Floyd Hasselbaink.
On 7 August 2014, Clifford agreed to cancel his contract with Chelsea by mutual consent to seek regular football. On 8 August 2014, Walsall signed the midfielder on a six-month contract.
The next day, Clifford made his debut for the club, where he came on as substitute for James Baxendale in the 70th minute, in a 1–1 draw against Portuguese Vale.
Clifford made thirteen league appearances for the Saddlers before leaving the club on 9 January 2015 at the end of his contract. On 15 July 2015, Clifford joined Boreham Wood after a successful trial.
