(Last edited Oct. 3 2021)
 

I started coaching softball at the coach pitch level in 2012 with no knowledge of the rule differences between baseball and softball. This was not a problem at all for coach pitch and Minors AA. It was not until my daughter was at the AAA level that it became apparent other teams were taking advantage of rule differences I didn't know. So I put the following list together as a reference for our coaches. 

• “Look Back” Rule: This is the most significant rule difference. When the pitcher has the ball and enters the 8' (radius) circle around the rubber (which must be marked), any runner not on a base must immediately return to a base or try to advance. (Penalty: Runner is out.) A runner cannot do both, i.e., begin to return or advance and then reverse direction, unless the pitcher attempts (or fakes) a play on the runner. Having the ball within the circle does not prevent an advancing runner from continuing. (Rule 7.08(a)(4))  ***Make sure you know this rule before playing in a town that uses softball-trained umpires. Also, I have never seen a baseball-only umpire make this call, so other towns may give you or our umps a hard time during our home games if it is not called.***
   
• The runner is out for leaving base before the pitch reaches the batter (Minors) or is released by the pitcher (Majors and Juniors). (Rule 7.08(a)(5))  
  • Related to this rule: Many aggressive teams will have the batter overrun first base on a walk, in other words try to advance to second base. If the catcher cannot throw the runner out it is important to get the ball back to the pitcher in the circle to put the runner in jeopardy of the aforementioned “Look Back" rule.​
     
• Pitching motions. A pitch must be delivered with an underhand motion, the wrist no further from the body than the elbow. The pitcher begins with her shoulders square to home plate, her pivot foot on and her free foot on or behind the rubber. A backward step with the free foot can be taken before or as the hands are brought together. The pitcher may use a “windmill” delivery – the arm makes a complete forward circle, and the ball is released on the second forward motion, or a “slingshot” delivery – the arm goes back and up, and the ball is released on the first forward motion. In either delivery, a forward step is taken with the free foot. The pivot foot may drag off the rubber as the pitch is delivered, but the pitcher may not drag or “crow hop” the pivot foot to a new spot ahead of the rubber and push off from there, nor leap and deliver the ball with the pivot foot in the air. (Rule 8.01)
   
• Pitching rule violations are illegal pitches, with a ball called on the batter. The offense may elect to decline the penalty and take the play. If the batter and all runners advance at least one base, the illegal pitch simply is ignored. There are no balks. (Rule 8.01)
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• The batter’s box is 7' long (not 6’ like baseball; there is an extra foot ahead of the plate) (Rule 1.04)
   
• Pitching distance is 35' for Minors, 40' for Majors and 43' for Juniors. (Rule 1.07)
   
• Individual players may choose to wear or not wear a cap or visor (Rule 1.11)
   
• The catcher can wear a catcher’s mitt, first baseman’s mitt, or fielder’s glove. (Rule 1.12)
   
• Hit by Pitch: A softball hitter must attempt to avoid the ball hitting them. No base is awarded – the pitch is a ball. (Note: This rule is the same for baseball, but it is called more frequently in softball. My guess is it's because the pitches are coming in slower.)
   
• Not specific to softball, but a rule I have seen coaches and fans lose their cool for not knowing: A runner is not out when contacting a batted ball if either the ball went through or past the fielder untouched, or if the ball was first deflected by a fielder. However, the runner is out if they intentionally kick or interfere with a ball in play. 

-Bill Kelly