Why did he always pick up the dirt before every fight?

This is because he is a farmer. The sand and dirt define him. They make him who he is. The land gives him trust and strength.

Better grip.

He uses it like lifters use chalk, for grip.
It might also have become a ritual pre-fighting.

http://www.newsday.com/sports/baseball/mets/rookie-darrell-ceciliani-delivers-for-mets-1.10551010

Shadows and dust. As a soldier and a gladiator, he was that close to death every time he picked up his sword. Also, better grip.


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You'll Never Walk Alone

its for grip on the sword, he doesn't want it to slip out from sweaty palms, just like rock climbers using chalk for grip. same thing

Same reason baseball players do it.

There are no "theories" on this.
It removes current & prevents sweat to come in your hand palms.
Today, powdered magnesium is used by weightlifters & such. (Not many ancient, melee weapon fights going on nowadays.)

There may be a secondary ritual; "The battle starts now." Anyhow, that is "secondary." The dust & dirt/gravel serves a very practical purpose.