to Sharapova hitting high numbers of double faults. Two-time US Open singles champion Tracy Austin stated that Sharapova often lost confidence in the rest of her game when she experienced problems with her serve, and consequently produced more unforced errors and generally played more tentatively, whilst tennis writer Joel Drucker remarked that her serve was the "catalyst for her entire game", and that her struggles with it left her "unmasked." In her return from an injury layoff in 2008 to 2009, she used an abbreviated motion, which, whilst producing aces, was somewhat less powerful, and also gave a very high number of double faults. From 2010, Sharapova returned to a more elongated motion, similar to her pre-surgery serve. She was able to produce speeds greater than before, including a 121 mph (195 km/h) serve hit at the Birmingham tournament in 2010 – the fastest serve of her career. Continuing shoulder injuries affected her serve, and, by the end of her career, her serve was a major liability, with Sharapova serving many double faults per match. Sharapova was thought to have good speed around the court, especially considering her height, although her footwork, speed, and court coverage were always considered the major weaknesses in her game. These improved throughout her career, allowing her to execute a more defensive playing style effectively, counterpunching until she could create the opportunity to hit a winner. Throughout her career, Sharapova's greatest asset was considered to be her mental toughness and competitive spirit, with Nick Bollettieri stating that she is "tough as nails"; Bollettieri later described her mental strength as "unbelieveable". Hall-of-famer John McEnroe said of Sharapova, "she's one of the best competitors in the history of the sport." Upon her retirement, she was described as "the ultimate competitor", who was set apart from her peers by her mental strength, and was lauded as an "unyielding character". American player Christina McHale described playing Sharapova as "intimidating" due to her mental fortitude, competitive spirit, and composure under pressure. Sharapova was known for on-court "grunting", which reached a recorded 101 decibels during a match at Wimbledon in 2005; Sharapova described her grunting as "a natural instinct." When questioned by the media about her grunting, Sharapova urged the media to "just watch the match." Because she predicated her game on power and aggression, Sharapova's preferred surfaces early in her career were fast hard, grass, and carpet courts. Sharapova initially