Peter Alonso could be in for a big rookie year

Last season, the Mets had an obvious hole at first base. Hitters at that position slashed .251/.302/.407 for a 94 wRC+ and compiled -0.3 fWAR. The Mets’ offseason strategy so far hasn’t been to address this hole. Instead, they’ve stockpiled second basemen in hopes of turning them into super utility types, in part because versatility is hot right now, but also because they might already have their first baseman of the future in Peter Alonso.

For a while, it looked like Alonso would be blocked by Dominic Smith, but Smith’s struggles and Alonso’s surging performance have reversed their fortunes. MLB Pipeline ranks Alonso as the top first base prospect, and second overall in the Mets organization. Though he wasn’t given a September call-up, Alonso could be in line for the starting first baseman role coming out of Spring Training (or after the Mets have sufficiently manipulated his service time).

PECOTA lists Alonso as one of the two position players with the highest breakout rate at 20 percent. Breakout rate, as defined in the BP Annual is “the percent chance that a player’s production will improve by at least 20 percent relative to the weighted average of his performance over his most recent seasons.” Often, players with high breakout rates will have lackluster projections. Miami’s Joe Dunnard, who shares the top of the breakout leaderboard with Alonso is projected for -0.6 WARP. It’s not hard to be 20 percent better than below-replacement.

Alonso, however, is projected for 1.3 WARP over a little more than half a season’s worth of plate appearances. Steamer/600 has at 1.9 fWAR, which is pretty good for someone who just turned 24 in December. Even with the crowded Mets infield, Alonso could force his way into an everyday role. An Alonso breakout could create the sort of problem that other teams would love to suffer through: having too many good players.

Looking at Alonso as a hitter, there’s a lot to like. The obvious thing is his power. Across Double-A and Triple-A last year, he hit 36 homers and his lowest ISO was .231 at High-A St. Lucie. He handles high velocity well because of his compact swing. Until his promotion to Triple-A, Alonso hadn’t posted a strikeout rate higher than 18.5 percent at any level. Even the jump up to a 25.9 percent strikeout rate was something that he improved as the year went on.

Alonso has even shown he’s capable of drawing more walks. In 2018, he maintained a 13.2 walk rate across two levels. PECOTA and Steamer project him for a walk rate between 9 and 10 percent, which is certainly manageable if he can maintain an above average strikeout rate.

Alonso isn’t without his faults. His defense limits him to first base, and his lack of versatility could keep him on the bench if Jeff McNeil, Jed Lowrie, and Robinson Cano are all playing well and needing playing time. It’ll also be interesting to see how major league pitchers approach him. It’s thought that he might be susceptible to fastballs above and below the strike zone.

Until he debuts, we won’t know whether Alonso will follow in the footsteps of Rhys Hoskins or Chris Carter. He could be a dinger-mashing clank-mitt that mashes enough to remain viable, or he might be the kind of player that leads the league in homers before getting DFA’d. The Mets are hoping for the former.

Kenny Kelly is a writer for Beyond the Box Score and McCovey Chronicles. You can follow him on Twitter @KennyKellyWords.