Troy Tulowitzki has been outrageously hot at home, but he isn' the only Colorado star crushing the ball in Denver. (Robert Beck/SI)

Though they have only briefly claimed a share of first place in the NL West, the Rockies have been one of the majors' most surprising teams thus far. Coming off three straight losing seasons, they bolted out to a 21-14 record before a 2-5 road trip through Texas, Cincinnati and Kansas City brought them back to earth. On Friday night, they return to Coors Field. Not only have they gone 13-5 there this year, they're putting up video game offensive numbers that recall the park's pre-humidor days.

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Justifiably, Troy Tulowitzki's out-of-this-world performance (.391/.497/.750, including an insane .608/.677/1.098 at home) has garnered most of the attention. All three of those full-season slash stats lead the league, as do his 11 homers and 221 OPS+, making him the early leader in any MVP discussion. Meanwhile, Charlie Blackmon's out-of-nowhere performance (.333/.366/.582, including .414/.440/.800 at Coors) has placed him in the top five in several key offensive categories, Nolan Arenado (.315/.343/.515) recently reeled off a club-record 28-game hitting streak and Justin Morneau (.320/.346/.571) is showing his best form since a 2010 concussion derailed his career. As a team, these purple pitcher-eaters are getting better-than-average production (OPS+ above 100) at every position but catcher and second base.

The team's mile-high environment is helping to inflate those numbers, of course. The Rockies have scored a jaw-dropping 7.67 runs per game at home thus far while hitting .353/.399/.598. Obviously, we're dealing with small sample sizes here (22 percent of the home schedule) but such numbers haven't been seen at Coors since the days of Dante Bichette and Vinny Castilla. The Rockies' home batting average, slugging percentage and OPS would all be team records, but amazingly, that scoring rate would rank only third:

Rk Season AVG/OBP/SLG OPS RPG 1 1996 .343/.408/.579 .987 8.12 2 2000 .334/.401/.538 .939 7.81 3 2014 .353/.399/.598 .997 7.67 4 1999 .325/.383/.549 .932 7.06 5 2001 .331/.387/.554 .941 6.84 6 1995 .316/.383/.556 .939 6.74 7 1997 .321/.386/.523 .909 6.73 8 1998 .325/.382/.519 .901 6.49 9 2003 .294/.372/.503 .875 6.38 10 2002 .313/.376/.496 .872 6.15

Most of those numbers hail from a bygone era of higher scoring, not only before the humidor was introduced in 2002 to help mitigate the effects of playing so far above sea level but also when pitchers with intact and seemingly invulnerable ulnar collateral ligaments struggled in vain to keep overmuscled sluggers in the park. Put in the context of contemporary offensive levels, the 2014 Rockies' early-season performance towers like Pike's Peak (elevation 14,115 feet) over the rest of the majors:

Rk Season Rockies @ Coors MLB Home OPS+ 1 2014 .353/.399/.598 .251/.317/.393 178 2 1996 .343/.408/.579 .270/.340/.427 156 3 1995 .316/.383/.556 .267/.338/.417 147 4 2001 .331/.387/.554 .264/.332/.427 146 5T 1997 .321/.386/.523 .267/.337/.419 139 2000 .334/.401/.538 .270/.345/.437 139 2012 .306/.367/.500 .255/.319/.405 139

For as much as those early editions of the Rockies could light up scoreboards, it's worth remembering that the team didn't enjoy a whole lot of success, because their own pitchers were no more effective at shutting down opponents. Only one of the Colorado teams in the above table reached the playoffs, and that one, the 1995 NL wild card winners, did so in a strike-shortened season. The most wins of any of those clubs was 83, a franchise record that held until the 2007 club that finished the regular season on a 14-1 tear (including a Game 163 tiebreaker that gave them the wild card) and then won the NL pennant. Those Rockies scored "only" 5.83 runs per game at home, the seventh-lowest rate in team history, but yielded just 4.83 runs per game. The 2009 NL wild card winners, Colorado's only other playoff team, averaged 5.73 runs per game while allowing just 4.41, the third-lowest rate in team history.

Underlying the Rockies' success thus far is the NL's top run differential (+50), helped along in part by holding opponents to 4.61 runs per game at home, beating out the 4.68 per game allowed by the 2009 and '10 teams. Relative to the league, those numbers aren't particularly sexy; in fact, Colorado has just two starters who have prevented runs at a better-than-average rate in Jordan Lyles (2.66 ERA, 159 ERA+) and Juan Nicasio (3.77 ERA, 112 ERA+); the rest of the rotation has ERAs and FIPs above 4.45.

Taken together, offense at Coors Field is at levels unseen for a decade or more:

The lighter solid line is the OPS+ of the Rockies and their opponents for a given year, via the formula 100*[OBP/lg OBP + SLG/lg SLG - 1]; I'm using the entire MLB as the league, which approximates the tOPS+ stat here. The dark purple line is the ballpark's single-year park factor from Baseball-Reference.com; 100 is the major league average, and since Coors has never produced below-average offensive levels, I've done away with that portion of the entire graph, which distorts the scale. The dotted line is B-Ref's three-year park factor, which is what generally gets used in the adjustments for Wins Above Replacement and other advanced metrics, since one year of data isn't a reliable sample size due to the noise created by personnel turnover and randomness; note the year-to-year variance, with 2013 levels less inflated than 2012 or '14.

Also note that the way B-Ref calculates the park factor is fairly complex and excludes interleague games; the general idea is to estimate how inflated the levels would be if teams played 1/15th of their games there as a member of a 15-team league instead of 1/2. Other sources — such as the annual Bill James Handbooks and Baseball Prospectus — calculate park factor differently and in more granular fashion; the former publishes one- and three-year batting average and home run factors for left- and righthanded batters, while the latter supplies lefty and righty factors for batted ball (flies, grounders, popups and line drives) and hit types as well as scoring. Unfortunately, neither source offers 2014 data yet, so I've left it off the above charts, which is probably for the best given the sample sizes involved.

Indeed, the question as to why this year's offensive levels at Coors are so inflated owes less to any notion that the humidor is unplugged and more to the limited selection of opponents who have passed through Denver. Four of the six teams whom the Rockies have hosted rank among the majors' seven worst in run prevention: the Diamondbacks (30th at 5.26 per game), White Sox (29th at 5.10), Rangers (26th at 4.88) and Phillies (24th at 4.68 per game). Colorado itself is 20th at 4.36 per game. The Mets (15th at 4.22 per game) are nonetheless a hair worse than major league average (4.19 per game) with only the Giants (fifth at 3.52 per game) among the best teams at preventing runs. Of course, those teams' rankings owe in part to the beatings they suffered in Denver; all of the aforementioned opponents had at least two games at Coors where they allowed more than eight runs. Even stripping those games out, Arizona, Chicago, Texas and Philadelphia are among the bottom nine at run prevention, while San Francisco climbs to third in baseball and New York to 10th, which grants some credit to the Rockies' offense.

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