Judge Jack B. Weinstein concluded that, under US Law:
Poker is Predominated By Skill Rather than Chance
In his ruling, in United States of America against Lawrence Dicristina, he explains the evidence from the prosecution and defendant, who both agreed that poker has a significant amount of skill and a significant amount of chance. They agreed that the top players would eventually tend to come out ahead.
They differed as to how many would be ahead (e.g. if you were slightly better than another player, you may eventually do better than them, but still lose out due to the "rake").
They differed as to how long it would take to get ahead, and how long should be considered relevant. (Should the fact that a single hand is predominantly chance be considered, or the fact that after several dozens of hours played, the game is predominantly skill?)
The judge quotes precedence that
[t]he rule of lenity requires ambiguous criminal laws to be interpreted
in favor of the defendants subjected to them.
He draws on that rule of lenity to determine that this (rather meaningless, in my opinion) question should be decided in the defendant's favour.
Both the defendant’s and the government’s interpretations of the statute are plausible. It
is unclear from the text and legislative history of the IGBA whether every state gambling offense
would permit a federal conviction. See Part VI, infra. It is equally uncertain whether, in
enacting the statute, Congress foresaw that poker businesses would be prosecutable under it. See
Part VII, infra.
In light of these ambiguities, the rule of lenity requires that the defendant’s interpretation
be adopted, and his conviction be dismissed. His acts did not constitute a federal crime.