NASHVILLE, Tenn. -- The Chicago Cubs dramatically revamped their infield, signing Ben Zobrist to a four-year, $56 million deal and flipping Starlin Castro to the Yankees for pitching help, all in a matter of minutes.

In Zobrist, the Cubs gain a player who before 2015 ranked as one of the most valuable commodities in baseball. He is rarely seen as a big threat via more traditional metrics such as Triple Crown stats, never batting .300 or posting 100 RBIs in a season, but Zobrist at his best combines an impressive batting eye with solid gap power, baserunning prowess with excellent defense, along with a versatility that's enabled him to play more than 100 games at five positions during his 10-year major league career.

Zobrist will probably shelve most of that multi-position skill, at least for 2016, and take over as the Cubs' everyday second baseman. The Cubs are banking on getting something closer to either the pre-2015 version of Zobrist or the 2015 playoff version rather than what he offered during the regular season. From 2009 through 2015, Zobrist ranked fourth in the majors in Wins Above Replacement, a stat that seeks to measure all facets of the game but doesn't account for any added value derived from Zobrist's versatility. During Kansas City's October run to the crown, he batted .303/.370/.515, with a number of key hits throughout the postseason.

In between, Zobrist posted by far his least productive season as an everyday player. He missed 36 games last season, most of those because of a knee injury, which also appeared to hamper his production for a while after his return from the DL in late May. That marked the first time Zobrist played in fewer than 146 games since he became a big league regular in 2009. The knee injury also saddled Zobrist with the worst defensive numbers of his career and also his lowest Wins Above Replacement total as a full-time player.

The Cubs are betting that Zobrist can shake off last season's malady and stay healthy and productive through his age-35 to age-38 seasons. That's far from a sure bet, even if Zobrist's price tag looks a lot better than the $80 million range that had been briefly floated as a rumor earlier in the day.

The Cubs were already armed with enviable middle-infield depth, and their acquisition of Zobrist further enabled them to flip Castro to the Yankees for an effective arm and some salary relief. In Adam Warren, the Cubs nabbed a 28-year-old right-hander who can pitch out of the bullpen and in the rotation. That swingman profile has obscured some impressive, under-the-radar numbers. With Warren and Trevor Cahill both in the fold, the Cubs now have ample insurance should any of their starters get hurt, if Kyle Hendricks or Jason Hammel falters, or if the bullpen needs to soak up multiple innings to bail out a bad turn from any of the starting five.

On the other end of the trade, Castro had his share of defects: a shaky throwing arm that fueled copious errors when he played shortstop; an erratic offensive track record, including a .265/.296/.375 batting line last season; and a contract that guarantees him another four years and nearly $42 million. Still, he's 25, just a year older than Yankees second-base prospect Rob Refsnyder, who has failed to impress anyone at the major league level yet. Castro is also a three-time All-Star with nearly 1,000 career hits and has been one of the most productive middle infielders in the game during his better seasons.

Though the Cubs have now acquired John Lackey, lefty reliever Rex Brothers, Cahill, Warren, and Zobrist, they might not be done. Adding Zobrist could mean that Javier Baez is now expendable, too. As ESPN.com's Jesse Rogers reported, Baez’s name has come up in trade talks with multiple teams. Those inquiries make tons of sense: Baez is just 23; owns prodigious raw power, albeit with Grand Canyon-sized holes in his swing to match; can play multiple infield positions; offers six years of controllable service time; and will make the league minimum for the next two seasons. If the Cubs want to add a young pitcher with upside, Baez could be a key piece who could help make that kind of deal happen.

Still, even after losing out on David Price, the Cubs' seven-deep rotation doesn't look like much of a weakness. The more pressing need exists in the outfield. With center fielder and effective leadoff man Dexter Fowler a free agent, the Cubs have a key lineup spot to fill. The good news is that they have multiple options when it comes to filling it, whether or not they use Baez as trade bait.

Jason Heyward is the best remaining free agent on the market and also a perfect fit to replace Fowler, if the Cubs are confident his all-world defensive skills can translate to playing center field every day. At 26, Heyward would offer the kind of youth, stellar glove, and on-base ability that teams covet. The Cubs could also make a more modest investment in someone like Gerardo Parra, who is two years older than Heyward but also offers better-than-average defense, plus a strong bat against righties that could be leveraged into a strong platoon, if the Cubs can find a lefty-masher to complement him.

Coming off a run to the NLCS, the Cubs own a roster that's built to win both now and in the future, and they have some of the deepest pockets in the game. That means that even with their improved pitching depth and a free-agent market for starting pitchers that has thinned out considerably, snagging one more arm isn't out of the realm of possibility. Price, Zack Greinke, Jordan Zimmermann, Jeff Samardzija, Marco Estrada, J.A. Happ, and others are off the market, but Johnny Cueto, Wei-Yin Chen, Yovani Gallardo, Ian Kennedy and other capable starters remain in play.

Add it all up, and you have a team that's already been more active than most of its biggest NL rivals -- with the potential for another impact deal or two still to come.