Pop Warner told a different story on page 104 of his autobiography:
“When I was coaching at Cornell in 1897, I had the scrub team work the hidden ball play against the varsity in a practice game. The later in the season against Penn State, the hidden ball play was used for the first time in a game. In those days, Penn State was not as strong on the gridiron as they would later become and this game was merely a workout for Cornell.
“This play was used only once in the game and this was late in the fourth quarter after Cornell had already secured a big lead on the scoreboard….And the play worked like a charm. The Cornell ballcarrier untouched and scored a touchdown.”
Warner also wrote about how he had elastic installed in the hem of Charles Dillon’s jersey sometime before the 1903 Carlisle-Harvard game and how James Johnson placed the ball up the back of Dillon’s jersey after receiving the kickoff that opened the second half of the game. After Dillon crossed the goal line, another player (probably Johnson) removed the ball from his jersey and touched it down as was required by the rules at that time.
Determining the accuracy of Warner’s claim that his first use of the hidden ball play was in the 1897 Cornell-Penn State game could easily be verified by asking Joe Paterno as it would have happened early in his tenure in Happy Valley. Determining the accuracy of Heisman’s claim will be more difficult. It will likely require the perusal of newspaper coverage of the game by at least the Atlanta Constitution and the two schools involved. However, lack of mention in newspaper coverage doesn’t necessarily mean it didn’t happen because sportswriters often get things wrong.
I guess we will have to wait for Jeff Miller’s biography of Pop Warner to know who first used the hidden ball play.