By Thursday, Counsell was also calling out challenges – which he won’t be permitted to do during games – to help test the system further on the eve of the Cubs’ game Friday against the White Sox.

The Mets and all of MLB will need to adjust to the new ABS challenge system. Here's a primer on the essentials of the system ...

MLB players can now challenge balls and strikes. But the Royals are being intentional about who gets to challenge.