Gregory Polanco has paid immediate dividends since being called up by the Pirates. He has, however, opted to forego a long-term deal, knowing arbitration in later years will likely be more financially beneficial. (Rob Foldy/Getty Images)

It seems to happen every year: A team with potential to contend calls up a young player, whose skills have been talked about endlessly but largely unseen, in hopes of changing a pennant race. In 2012, the Nationals called up Bryce Harper, stuck him in center field, and away they went to the National League East title. Last spring, the flailing Dodgers called up Yasiel Puig, found a spot for him in a star-studded outfield and went on a 42-8 run en route to the NL West crown.

On Monday, the Pittsburgh Pirates — struggling under .500 — reached into their own deck and played their most intriguing card. When veteran Neil Walker went down with a concussion, they called up 22-year-old outfielder Gregory Polanco and stuck him in the second spot in the lineup.

On Friday night, Polanco, who hit .347 and drove in 49 runs in his first 62 games at Class AAA, went 5 for 7 and hit his first big league homer, a two-run shot in the 13th inning that provided the difference in a victory at Miami. In his first four games, he went 8 for 21.

“It’s fun to watch,” Manager Clint Hurdle said. “He’s been taking it in stride. He’s very grounded. He knows there are things he can continue to work on.”

That was the franchise’s stock line as Polanco toiled at Indianapolis. But his situation, and those of other top prospects, is instructive about the vagaries of baseball’s financial system.

In general, clubs have control over players for their first six years in the big leagues. In most cases, the club completely controls a player’s salary during the first three seasons, and a player is eligible for arbitration for years four, five and six. Thus, the largest jump in salary comes between year three (when a player’s salary is not much more than the major league minimum) and year four (when his salary becomes comparable with other players of similar statistical achievements through arbitration).

The difference — and the reason some get suspicious of teams not calling up top prospects until June — is that, through a process known as “Super 2,” players who have between two and three years of major league service time can be eligible for a fourth year of arbitration — and, thus, a fourth year to make millions of dollars before becoming a free agent. The top 22 percent of players between two and three years of service time are awarded the extra year of arbitration.

Polanco’s situation is instructive of another trend: trying to sign prospects to long, team-friendly contracts before they make their major league debuts. The Astros were successful with first baseman Jonathan Singleton (five years, $10 million, eight and $35 million with team options) but unsuccessful with outfielder George Springer (seven years, $23 million).

Declining such a deal can be confusing to fans but makes absolute sense for players. Polanco reportedly turned down a seven-year, $25 million deal. Why? Salaries in arbitration will certainly rise by the time he is eligible to enter the system.

Pirates fans can now enjoy a summer with Polanco, wondering whether — like Harper and Puig — he can help his team contend. But they are also learning a hard lesson of team construction — trying to lock up the prospects who figure to become their best players before they have fully arrived and why so many players resist it.