What stage of the scientific method will someone be at if they make a prediction that drinking alcohol will make people more violent during a sporting event?

Forming a testable hypothesis

Explanation:

Hypothesis can be defined as an answer to a scientific test.

Testable Hypothesis is the stage in the scientific method in which testing and data collection is done and based on these data, a hypothesis is either proved or disproved.

In the given case, the stage at which the person will be at when he/she predicts violent behavior caused by drinking habit is "Forming a testable hypothesis". The person will collect data on the violent behaviors of sportsmen during a sporting event and analysis if they have drinking habits or not. And based on the collected data will either prove or disprove with the given hypothesis.