8th inning 7th inning. Its all high leverage. Unless you're thinking of just dumping Barnes altogether. And if kelly didn;t throw 100 pitches in his inning yesterday, he might have gotten another.
This, and...I suspect Farrell is thinking of leverage in more sophisticated terms than just inning. Last night Kelly faced Carter, Gardner, Sanchez, with Judge waiting if somebody gets on. Barnes faced Holliday, Castro and Hicks. Both pretty good groups of hitters, but which would you reserve your better reliever for?
The last time they were both used in the same game was May 29 vs. the White Sox, and very much the same deal: Kelly was brought in in the 7th to face the White Sox' 3-4-5-6 hitters, Barnes in the 8th to face the bottom of the order.
The time before that, May 17, Barnes was brought in in the 7th with the Sox trailing, faced one batter, and then when the Sox tied the score in the top of the 8th, Kelly was brought in to hold the lead.
The time before that, May 11, Kelly came in the 7th to face 3-4-5, and Barnes in the 8th to face 7-8-9.
As those dates show, Kelly and Barnes aren't actually being used in the same game very much, which suggests that Farrell sees them as filling essentially similar roles. But when they do appear in the same game, the recent record shows Farrell choosing Kelly to face tougher hitters and/or in higher-leverage situations.