Often times coaches promote their playing background as credentials to prove their worthiness. It is as if being the #1 player in the world instantly qualifies them to be the #1 coach in the world.
I think playing a sport is a critical part of becoming a great coach. However, in my sporting experiences the most naturally gifted athletes tend not make the best coaches. Instead, it is those coaches that had to struggle, fail, learn and work extremely hard just to succeed in their sport who make the best coaches. It is almost as if since they have made so many mistakes and failed so many times along the way those failures actually become assets. You see when you have failed so many times and in so many different ways it makes it easy to spot the exact mistake an athlete is making. It is the accumulation of failures that serves as education for a future hall of fame coach.
For example, take perhaps the greatest baseball hitting coach you never heard of, Charley Lau. Charley had an average career in the major leagues and certainly did not set any records for hitting. After his playing career was over he went on to become one of the greatest and most sought after hitting coaches of all time. I guarantee Coach Lau would not have been so great had he not learned so much from so many of his failures. In fact, it was all his failures and struggles that allowed him to see things about hitting in a way no one else could.