WASHINGTON -- The Washington Nationals have banned backpacks from their ballpark, a step farther than other major league clubs have gone in an era of enhanced security at stadiums.

The Nationals announced the change Friday. It will take effect starting this season.

All major league ballparks require fans to pass through metal detectors. Most teams have limits on bag size but don't restrict a particular type of bag. But under Washington's new policy, even backpacks that are within the size requirements for other bags will not be permitted.

Exceptions will be made for backpack diaper bags or knapsacks used for medical reasons or for the aid of people who are disabled. People who bring those bags, though, will need to obtain a waiver at the gate before entering Nationals Park, which is just over 1 mile south of the U.S. Capitol.

"We are constantly assessing our procedures in an effort to make our ballpark safer," Scott Fear, the Nationals' president of public safety and security, said in a statement. "We understand the implementation of these procedures will take some time for our fans to get used to, but our organization is dedicated to making Nationals Park the safest environment possible for everyone in attendance."