Rockies rookie Elehuris Montero is an aggressive hitter, there can be no denying that.

In the fourth inning of the Rockies’ 12-6 loss to Arizona on Sunday, he ambushed Zac Gallen’s first-pitch cutter, driving it into right-center field for a two-run double.

Considering how well Gallen has pitched this season, Montero’s aggressive plan of attack made sense. Gallen, after all, is 12-2 with a 2.50 ERA, and his 0.908 WHIP and 5.9 hits allowed per nine are the best in the National League.

“To do what he did against Gallen, arguably one of the best pitchers presently in the game, driving the ball to right-center on a cutter, is a good sign,” manager Bud Black said. “And it’s a positive that he can take (from that game).”

A number of Rockies players have made their big-league debuts this season, including first baseman/right fielder Michael Toglia and catcher Brian Serven. It’s Montero, however, who’s had the biggest impact. Standing 6-foot-3 and weighing 235 pounds, Montero is “country strong,” as Black put it.

Entering Tuesday night’s game in Chicago against the White Sox, Montero is hitting .257 (35-for-136) with five home runs, 14 doubles and 17 RBIs. He’s played in 41 games since his May 1 debut, starting 15 games at third base, 11 at first base and 10 as the designated hitter.

He remains a work in progress in the field, as a sloppy throwing error from third base in the fourth inning of Sunday’s game illustrated.

But there is no denying his power at the plate.

“When he barrels a ball up, you know it,” third baseman Ryan McMahon said. “The ball explodes off his bat and he’s got a solid swing, too.”

But there are holes in Montero’s approach at the plate that require plugging. His 32.9% strikeout rate vs. a 4.2% walk rate, plus his .294 on-base percentage, are numbers that reveal a work in progress.

Montero’s at-bat in the eighth inning Sunday against Arizona All-Star lefty Joe Mantiply illustrated how far Montero has to go. From the outset, Mantiply had Montero fishing at off-speed pitches, ultimately whiffing him on a 3-2 bender.

“Mantiply’s an All-Star with good secondary stuff — a slider and a change, down below the zone,” Black said. “That’s the thing that ‘Monty’ needs to work on. He’s had a tendency to swing at the low, soft pitch. That’s where the challenge is moving forward. But he’ll get there.”

On Deck

Rockies RHP Chad Kuhl (6-8, 5.38 ERA) at White Sox RHP Michael Kopech (4-9, 3.78)
6:10 p.m. Tuesday, Guaranteed Rate Field
TV: AT&T SportsNet
Radio: KOA 850 AM/94.1 FM

Kuhl, who’s scheduled to become a free agent at the end of the season, has been struggling. In his last start, the Rockies rallied for a 10-7, 10-inning victory over Milwaukee, but the right-hander gave up five runs on six hits in 4 1/3 innings, including a 499-foot homer to Christian Yelich. Since his complete-game shutout of the Dodgers at Coors Field on June 27, Kuhl is 1-4 in nine starts, posting a 9.08 ERA, allowing 15 home runs over that span for an average of 3.40 home runs per nine innings. Kuhl has never pitched against the White Sox.

Kopech, who was on the 15-day injured list from Aug. 23 to Sept. 7 with a left knee strain, will make his 25th start of the season. He’s winless in his last six starts, going 0-3 with a 5.88
ERA, but he had 24 strikeouts over that span while holding hitters to a .221 batting average. He got a victory in Chicago’s 2-1 win over the Rockies on July 26 at Coors Field, pitching 5 1/3 scoreless innings, giving up six hits, walking three, and striking out four. That’s the only time he’s faced the Rockies.

Trending: C.J. Cron has an RBI in four straight games and 10 total RBIs through his last eight games. His 96 RBIs lead the team.

At Issue: Veteran outfielder/designated hitter Charlie Blackmon is in a slump. On the just-completed homestand, he hit 2-for-20 with five strikeouts and his average has slipped to .260.

Pitching probables:

Wednesday: Rockies LHP Kyle Freeland (8-9, 4.63) at White Sox RHP Dylan Cease (14-6, 2.06), 12:10 p.m., ATTRM
Thursday: Off day