+100% Speed bonus.
"Faster pussycat, Kill, KILL KILLLLLLL."
A few examples show that troopers with Sprinter have a better bullet dodging rate when moving, which is quite similar to Zigzag.
A trooper with Sprinter does well in Defender style. He can quickly move back from the enemy's firing range, or move into the enemy's minimum firing range, to disrupt the enemy's Aim and attack. The constant moving also gives a significant penalty to the enemy's Aim.
It is well known that Minitroopers has many translation mistakes. This is the original French description for the Sprinter skill...
"+100% en vitesse de déplacement" the word for word translation of this would be...
"+100% in speed of movement".
However, the current English version of Minitroopers has had this mistake corrected. Furthermore, the original French description may not be a translation error so much as a grammatical one.