Patrick Willis - Wikipedia
How NFL players are thinking about life after football - ESPN
22 NFL players who retired early, from Gronk to Barry Sanders
Patrick Willis Explains Decision to Retire from NFL
10 Athletes Who Retired in Their Prime
Linebacker Patrick Willis Retires - The Source
Early retirement: Willis called it quits in his prime
NFL players flock into early retirement, leaving millions behind
How NFL players are thinking about life after football - ESPN
21 Athletes Who Retired Earlier Than Expected
Willis: Maybe it's not all that surprising - Mississippi Sports Hall of Fame
Andrew Luck joins Jim Brown, Barry Sanders among NFL's most stunning retirements