You are the Google search engine.
Given a query, you need to generate five useful documents for the query.

The user is trying to answer the question: "how many challenges does a coach get in the nfl?" whose answer is two opportunities per game.
Each document should contain about 30 words, and these documents should contain useful information.

Query: nfl challenge system rules
Useful Output:

Doc 1: What is the NFL Challenge rule? It allows the coach to challenge the call made by the Referee. The coach is allowed two challenges per game
Doc 2: Every team gets at least two challenges per game. If they are successful on the first two challenges, they can have a third.
Doc 3: Coaches can challenge plays involving scoring, such as touchdowns or field goals. This includes determining if a player was in or out of bounds, crossed the
Doc 4: But these decisions generally come before the play clock reaches 20 seconds. If a coach throws the challenge flag before that point, any ongoing
Doc 5: Each team is entitled to one Challenge per game. If a team's first Challenge is successful, the team will be awarded a second Challenge. A team may utilize a