As a rookie in 1948, Tunnell appeared in 10 games and intercepted seven passes, including one returned 43 yards for a touchdown. Between 1949 and 1952, he was known as one of the best pass defenders and punt returners in the NFL. He was a key element in the Giants' famed "umbrella defense" that shut down the passing game of opponents in the early 1950s, and he was referred to as the Giants' "offense on defense". His accomplishments during those prime years include the following: