For Leon, who didn't arrive from Nashville until 5 p.m. PT, it was his second stint with the A's. The first one also lasted all of one day, but it didn't include an appearance, since he was simply the 26th man on the roster for a doubleheader. At the time, Leon was considered an option to start one of those games, so he flew his parents in from Mexico.
On Wednesday, there was no time for them or his wife and child to get to Anaheim. But he does have a souvenir for them, taking with him the ball he got Angels outfielder and former Triple-A teammate Collin Cowgill to swing through for a game-ending strikeout.
"It's really special," said catcher Stephen Vogt. "I've caught Arnold for parts of the last couple years, and what a great person he is, what a great pitcher. To see him make his debut, especially after what happened last year, it's a lot of fun. When I saw him warming up tonight, it put a smile on my face."
Leon allowed one run on two hits in his lone inning, which began with Mike Trout flying out to shallow center.
"As soon as I realized Trout was coming in," said Leon, smiling, "I said, 'Wow. I'm going to throw it right in the middle and see how far he's going to hit it.'"
"Just awesome," said A's manager Bob Melvin. "Arnold has been here twice now and not very long, and to get him in a game like that, get him part of it … we're going to make a corresponding move and send him down tonight, but I was glad we could get him in a game and get him that experience. Now he knows what it's like to pitch in the big leagues, and when he's back, he'll have that already behind him."
Leon, who took the roster spot of right-hander R.J. Alvarez, he of a 12.00 ERA in six appearances, will head back to Triple-A Nashville to make room for right-hander Chris Bassitt, who is expected to be available in long relief in time for Thursday's series finale.
Jane Lee is a reporter for MLB.com. Read her blog, Major Lee-ague, and follow her on Twitter @JaneMLB. This story was not subject to the approval of Major League Baseball or its clubs.