I am in a tournament for my western civilization class. The tournament is called "Most Influential Leader Tournament." You are randomly given a leader from a division based on your class period. I'm the 5th seed with Ataturk, founder of Turkey, against the 1st seed with Gandhi. It does not matter if the person did good or bad things; it matters if they were influential. I will be graded on these 6 critiques: impact, influence, inspiration, presentation, goals met, & uniqueness of the person.
Not only do I need to fight for Ataturk, I also very much need to defend him and fight against Gandhi.

What I would do I make a chart with major items like laws or family life or business or government or whatever he influenced listed on the side of the chart. Then I would read everything I could about him and fill in the chart. That will giving you your debating points.

Try to find the positive traits and influence of Ataturk, his achievements, methods, personality etc. his influence on particular community, people, region etc.

It will be difficult to argue against Gandhi.
I don't understand why defending one influential person requires going against another, when they weren't fighting each other or competing for anything. This isn't a debate about pros and cons of something like eating meat, where one side is truly 'against' the other in debate.
I would say so.
I don't care for this 'debate' particularly, if it really is as you say. Present your arguments for most influential on the person's merits, and refuse to malign the other influential person.

My teacher told us to be able to fight against the opponent's influence.

my teacher told us to be able to fight against the opponent's influence.
Then make a chart with Gandhi heading one column and Ataturk heading the second column with the various spheres of influence running down the left. Compare and contrast to make your case.

Influences... Gandhi... Ataturk
violence
Human rights
Religion
Culture
Race
Politics