Hisense Sharks second rower Reece Williams has announced his retirement from professional rugby league effective immediately. <br><br> Williams played 98 NRL games for the Cronulla club after making his first grade debut in 2003, but after suffering a series of head knocks that left him hospitalised twice in the past eight months, the 25-year-old has been forced to hang up the boots. <br><br> "I'm shattered to have made this decision, but I had no other choice under the doctor's advice," Williams said. <br><br> "The last few months have been very hard to take but at the same time I'm excited about the journey ahead and starting a new career." <br><br> Sharks head coach Shane Flanagan, whose squad returned to training yesterday for the 2011 season, said it was disappointing Williams' career had to end prematurely. <br><br> Williams will now turn all his attention to his personal training business, 'Williams Workouts', a business he recently started in the Sutherland Shire.