What Justin Martinez has been doing this winter is extremely encouraging for the Arizona Diamondbacks, and the recent buzz around the right-handed flamethrower is the latest example.

With the major league season concluded, many players are participating in winter ball. Martinez is one of them, after only appeared in 15 games (pitching 13.1 innings) with the Diamondbacks last season due to elbow surgery.

And on Tuesday night, pitching for Aguilas Cibaenas, the young fireballer hurled what was the hardest recorded pitch in his career — at least according to the Statcast readings.

Justin Martinez throws fastest pitch of career

Pitching in the seventh inning of a game against Tigres del Licey, and facing an 8-6 deficit, Martinez fired a sinker to Chicago Cubs outfielder Kevin Alcantara.

The offering read 104.2 MPH, the hardest pitch thrown by Martinez in his career.

While he's always been able to hit triple digits consistently, it's worth noting he averaged 101.6 MPH on his four-seam fastball and 101.8 MPH on his sinker, which has become the more primary of his two fastballs over the past several seasons.

The velocity reading that high is a good sign of where Martinez's health is, currently. Sometimes, Tommy John surgery can affect a player's velocity and command. Martinez hasn't seemed to miss a beat in that regard, and now appears to be throwing even harder than before.

Obviously, velocity is important in today's era of baseball. It's the biggest reason Martinez has 145 strikeouts over 111.1 career innings in the majors.

But 104.2 MPH isn't the number that stands out the most from Martinez's winter league activities. There's one that is even more encouraging for the future of the Diamondbacks' bullpen.

Justin Martinez limiting base traffic in winter league action

Granted, Martinez is playing against slightly less intimidating competition than entire teams made up of major league players.

But he's also not walking anyone.

In six games for Aguilas Cibaenas, Martinez has allowed only four base hits. He has not walked a single batter and his WHIP is a stellar 0.67. He's struck out eight batters in the process.

Those who know Martinez are well aware that his electric stuff can often deviate far from the zone. He's had an issue with walks — as many high-velo flamethrowers do — even when pitching effectively.

In his MLB career, Martinez has walked 69 batters for a BB% of 14.2% and a BB/9 of 5.58. Those are very high. But strike-throwing ability has been seen at times; that was evident in 2026, when Martinez threw the second immaculate inning of Arizona's season toward the end of the year.

If he truly is dialing in his command, as these small winter sample size numbers suggest, to the point where that issue begins to tone itself down, the Diamondbacks don't just have an exciting bullpen arm. They have their future closer for years to come, barring more health issues, of course.