Many college players, even those who had high rankings as juniors, tend to drop significantly in the pro rankings once they enter college. That is because they play fewer professional tournaments while in school and therefore lose ranking points.

Axel Geller, 19, is an example. Geller, who is from Buenos Aires, was the No. 1-ranked junior in the world last year. But when he played for Stanford this season, he saw his ATP ranking fall to 1,416 — likely not high enough to get into next year’s Transition Tour events.

Geller said he agreed with the I.T.F. plan to winnow out fake pros. At one tournament last year, he was forced to play four qualifying matches to get into the main draw, where he promptly beat the No. 1 seed — a result that suggested he should have been in the main draw from the beginning.

“You will win matches if you are good enough,” Geller said. “The problem is when you are not able to get into the tournament.”

Tang, also 19, was ranked No. 59 in the world as a junior. But since going to college and playing fewer I.T.F. events, his ranking has fallen to 1,514, a figure that probably does not represent his true ability.

Like most college players, Tang was uncertain of the details of the complex new rules and what they will mean for him.

“It’s definitely something every tennis player should learn about,” he said, “because it is going to change the entire game, how people travel and how federations develop players.”