By TOM SHANAHAN Army football annals overflow with overachieving seniors that played backup and special teams roles until they seized their opportunity as a first-year starter. Jon Rhattigan is this year’s example. The senior linebacker that entered 2020 with six career tackles leads the Black Knights through four game with 28, 11 unassisted. His four tackles for a loss have totaled 20 yards; included are 1.5 sacks for 14 yards. “I'm really excited for Jon and happy with…