Walker had been on the IL since April 12 with a strained right oblique muscle.
"I'm very excited," Walker said. "[I've been] watching the games [on TV], and fortunately the guys have been playing well and winning so I've had a lot to cheer for from the couch, but I want to be in the dugout screaming and yelling and having fun. I'm just trying to be a piece [to] fit into this puzzle."
Walker's oblique strain was mild, so he was able to get back in the batting cage in relatively quick fashion. But even before he could swing, he stood in and tracked pitches in an attempt to keep his timing at the plate.
Locastro, meanwhile, was on the IL with a dislocated left pinkie finger, which he injured sliding into second base on a steal attempt April 17 in Washington.
It was the first time Locastro had been caught stealing in his big-league career after 29 straight successful swipes, and when he got up from his slide and looked at his hand he knew something was very wrong.
"Well, it was facing the opposite way normal fingers are supposed to face, so they had to pop it back into place," Locastro said. "And then the bone and stuff was [sticking] out a little bit, so they had to put some stitches on there."
Walker and Locastro were just a part of the lengthy list of injuries that the D-backs have suffered in the season's first five weeks. Despite it all, the team came into Tuesday's series opener with the Marlins having won six of its last eight and 10 of 13.
"It's very exciting, it's motivating, it's hopeful, it's all the good things," Walker said. "It's confidence-building because the guys know what they're capable of. It seems like every night somebody was getting the timely hit, or the big walk to extend the inning, and then when that stuff wasn't happening the [pitchers] were throwing well. I could tell what the vibe was like in the dugout by just watching the guys laugh and have a good time and everything's awesome when you win."
Soria activated; Kelly out
The D-backs also activated closer Joakim Soria from the injured list just before Tuesday's first pitch and placed right-hander Merrill Kelly on the injured list.
The team did not disclose why Kelly was going on the IL.
Soria has been on the IL since April 6 with a strained left calf, which he injured covering first base during the team's season-opening series with the Padres.
While Soria will take Kelly's roster spot, the D-backs will have to figure out who will take Kelly's spot in the rotation. Arizona is already short a starter with Taylor Widener on the IL (strained right groin).
Speaking of the trip...
First-base coach Dave McKay, who is still recovering from a broken rib and lacerated spleen suffered during Spring Training, is not with the team on this trip. On the recent homestand, McKay came to the ballpark for the first time and met with players in the afternoon before heading back home.
Hitting coach Darnell Coles is also missing the road trip as he recovers from a torn right Achilles tendon.