Question: The 2011 Grand Slam of Darts was sponsored by which London-based bookmaker?

Context paragraphs:
2008 Grand Slam of Darts: The 2008 Grand Slam of Darts was the second staging of the darts tournament, the Grand Slam of Darts organised by the Professional Darts Corporation.  The event took place from 15–23 November 2008 at the Wolverhampton Civic Hall.  As with 2007, the tournament included players from both the PDC and BDO organisations.

Williams sisters: The Williams sisters are two professional American tennis players: Venus Williams (b. 1980), a seven-time Grand Slam title winner (singles), and Serena Williams (b. 1981), twenty-three-time Grand Slam title winner (singles), both of whom were coached from an early age by their parents Richard Williams and Oracene Price.  There is a noted professional rivalry between them – between the 2001 US Open and the 2017 Australian Open tournaments, they met in nine Grand Slam singles finals.  They became the first two players, female or male, to play in 4 consecutive grand slam singles finals from the 2002 French Open to the 2003 Australian Open; Serena famously won all 4 to complete the first of two "Serena Slams".  Between 2000 and 2016, a 17-year span, they collectively won 12 Wimbledon singles titles (Venus won 5 and Serena won 7).  By winning the 2001 Australian Open women's doubles title, they became the 5th pair to complete the Career Doubles Grand Slam and the only pair to complete the Career Doubles Golden Slam.  At the time, Venus and Serena were only 20 and 19 years old, respectively.  Since then they have gone on to add another two Olympic gold medals in the 2008 Beijing Olympics and the 2012 London Olympics.  Nearly a decade later, the duo would go on to win 4 consecutive grand slam doubles titles from 2009 Wimbledon through 2010 Roland Garros, which would catapult them to co-No.  1 doubles players on 7 June 2010.  Two weeks later, on 21 June 2010, Serena would hold the No. 1 singles ranking and Venus would be right behind her at No. 2 in singles.  Their most recent grand slam doubles titles came at the 2012 Wimbledon & 2016 Wimbledon events.  They remain very close, often watching each other's matches in support, even after one of them has been knocked out of a tournament.

PDC World Darts Championship: The PDC World Darts Championship, organised by the Professional Darts Corporation (PDC), is one of the two World Professional Darts Championships held annually in the sport of darts.  The other is the BDO World Darts Championship organised by the British Darts Organisation (BDO).  The PDC championship begins in December, overlapping in January with the start of the BDO tournament.  The highest profile of the PDC's tournaments, it is held at Alexandra Palace in London and is sponsored by bookmaker William Hill; winners receive the Sid Waddell Trophy, named in honour of the legendary darts commentator Sid Waddell, who died in 2012.

Dave Chisnall: David "Dave" Chisnall (born 12 September 1980) is an English professional darts player from St Helens who plays in Professional Darts Corporation (PDC) events.  He began his career participating in the British Darts Organisation (BDO) and was the runner-up in their World Championship in 2010.  He switched to the PDC a year later and has won nine Pro Tour events.  Since his switch to the PDC, Chisnall is probably best known for defeating Phil Taylor in the 2012 World Championship, for reaching the final of the 2013 World Grand Prix where he was beaten 6–0 by Taylor and for reaching the final of the 2014 Grand Slam of Darts, losing a much closer match 16–13, again to Phil Taylor.  He hit his only televised nine-dart finish in the 2015 Grand Slam of Darts against Peter Wright.

2011 Grand Slam of Darts: The 2011 Grand Slam of Darts, the fifth staging of the darts tournament organised by the Professional Darts Corporation was known as the William Hill Grand Slam of Darts for sponsorship purposes.  The event took place from 12–20 November 2011 at the Wolverhampton Civic Hall.  For the first time, Sky Sports has given the television coverage of the Grand Slam after taking over from ITV Sport as the event's broadcaster.

Grand Slam of Darts: The Grand Slam of Darts is a darts tournament organised by the Professional Darts Corporation and is known as the bwin Grand Slam of Darts for sponsorship purposes.  The PDC also invites the best performing players from its rival, the British Darts Organisation.  There have been two previous head-to-head matches between the champions of the two organisation and a few overseas tournaments have also featured BDO v PDC clashes, but this tournament is the first of its kind to be held in the United Kingdom.

2010 Grand Slam of Darts: The 2010 Grand Slam of Darts was the fourth staging of the darts tournament, the Grand Slam of Darts organised by the Professional Darts Corporation.  The event took place from 13–21 November 2010 at the Wolverhampton Civic Hall.  Television coverage of the tournament was covered by ITV Sport, with live coverage on ITV4.  Although 8-0 down at one stage, Scott Waites made a remarkable comeback to defeat James Wade 16-12 in the final, becoming the first, and as of 2016, only member of the British Darts Organisation to win this event.

2009 Grand Slam of Darts: The 2009 Grand Slam of Darts was the third staging of the darts tournament, the Grand Slam of Darts organised by the Professional Darts Corporation.  The event took place from 14–22 November 2009 at the Wolverhampton Civic Hall.  Television coverage of the tournament was covered by ITV Sport, with live coverage on ITV4 and highlights on ITV1.  Despite being beaten by Vincent van der Voort in the group stages, Phil Taylor won a third consecutive Grand Slam with a 16–2 victory over Scott Waites.

William Hill (bookmaker): William Hill plc is a bookmaker based in London, England.  It is listed on the London Stock Exchange and is a constituent of the FTSE 250 Index.

2007 Grand Slam of Darts: The 2007 Grand Slam of Darts was the inaugural staging of the darts tournament, the Grand Slam of Darts, held by the Professional Darts Corporation.  The tournament invited the best performing players from the PDC and its rival the British Darts Organisation.  There had been two previous head-to-head matches between the champions of the two organisations and a few tournaments have also featured BDO v PDC clashes.  This tournament was the first of its kind to be held in the United Kingdom.

Supporting paragraphs: 2011 Grand Slam of Darts William Hill (bookmaker)
Answer: William Hill