One thing teams know about Marwin Gonzalez is that the free agent offers almost unparalleled defensive versatility, an attribute that is at the core of his appeal this offseason.
In 2018, Gonzalez started 65 games for the Astros in left field, 29 at shortstop, 21 at first base, 19 at second and two at third. Over seven seasons in Houston, he started at least 60 times at all five of those spots and did so capably, according to advanced metrics. It no doubt helps Gonzalez's case that he could fit in almost anywhere on the field, or continue serving in a super-utility role -- playing almost every day while moving around.
• The latest Gonzalez free-agent rumors
On the other hand, Gonzalez's bat would seem to come with many more question marks. Following a career year at the plate in 2017, the 29-year-old switch-hitter saw his numbers tumble in '18 to roughly league average, just as they'd been over the three previous seasons, from 2014-16.
Even if Gonzalez is only an average hitter, that, combined with his aforementioned jack-of-all-trades defensive status, should make him a desirable free agent. But before limiting his ceiling and dismissing 2017 as blip that can't be repeated, it's worth considering what happened with Gonzalez in the second half last season.
To sum it up, he started crushing the ball.
This is certainly visible in his surface-level results:
2017 season: .303/.377/.530 (144 wRC+)
'18 1st half: .230/.305/.355 (84 wRC+)
'18 2nd half: .275/.352/.492 (134 wRC+)
The change is perhaps even more noticeable in Gonzalez's hard-hit rate, which measures the percentage of his batted balls with an exit velocity of 95 mph or more, according to Statcast™. (In 2018, MLB players batted .524 with a 1.047 slugging percentage on hard-hit balls, compared with .223/.267 on those below the 95-mph threshold.)
2017 season: 36.6 percent
'18 1st half: 33.9 percent
'18 2nd half: 52.7 percent
Even in his terrific 2017 campaign, Gonzalez didn't have a standout hard-hit rate, and it dropped during his disappointing first half last season. After the break, however, it ranked fourth among nearly 250 batters who put 100 or more balls in play during that time, pushing Gonzalez just ahead of the likes of Giancarlo Stanton, Shohei Ohtani and Nelson Cruz.
Largest second-half gains in hard-hit rate
Min. 100 batted balls in both halves (208 batters)

1. Gonzalez: +18.9 percentage points (33.8 to 52.7)
   
2. Kole Calhoun: +15.3 percentage points (35.9 to 51.2)
   
3. Justin Turner: +12.7 percentage points (29.9 to 42.6)
   
4. Ronald Guzman: +11.8 percentage points (27.7 to 39.5)
   
5. Rougned Odor: +11.0 percentage points (32.3 to 43.3)
   Suddenly, Gonzalez was in uncharted territory. His hard-hit rates in August (54.9 percent) and September (53.4 percent) were by far his two highest in any month since Statcast™ began tracking in 2015.

The improvement was spread out, as well. Gonzalez posted at least a 50 percent rate as a right-handed batter and a left-handed batter, at home and on the road, and against fastballs and non-fastballs alike in the second half.
There were plenty of notable examples of Gonzalez's potent bat. On Aug. 6 in San Francisco, he launched a 103-mph, go-ahead three-run homer with the Astros down to their last out. On Sept. 9 in Boston, he ripped a 110.1-mph homer that ranks as his hardest base hit of the past four seasons. And in Game 2 of the American League Division Series against Cleveland, his four knocks included three of the hard-hit variety, among them a go-ahead two-run double in the sixth inning.
All of that potent contact suggests that Gonzalez's late surge in 2018 wasn't just a fluky hot streak. Of the 188 players who went to the plate at least 150 times in August and September, Gonzalez tied for fourth in expected slugging percentage with National League Rookie of the Year Ronald Acuna Jr., and ranked 10th in expected wOBA -- somewhere in between J.D. Martinez and Paul Goldschmidt. (These expected stats factor in a hitter's quality of contact.)

But the question now for interested clubs is how Gonzalez made those gains, and whether he can carry them into '19 and beyond. Late last August, Astros manager AJ Hinch pointed to Gonzalez being "in a good place with his hitting mechanics," and showing "exceptional" pitch selection. Indeed, Gonzalez increased his aggressiveness at the plate, boosting his swing rate against the types of in-zone pitches a hitter can square up most easily. That change was even more dramatic on the first pitch, and it might be that attacking more hittable pitches paid dividends.
"I think he has simplified his approach," Hinch said. "His strength of contact is really up. His pitch selection is better."
As Gonzalez looks to find a home for next season, his ability to handle so many positions is sure to be a primary selling point. But if the thump he showed late in 2018 carries over, he could prove to be much more than just a versatile defender.