A marginal increase in the NHL’s salary-cap ceiling and too many teams with limited cap space increases the risk of losing a restricted free agent to an offer sheet.

That was the lesson learned the hard way this summer by the Boston Bruins and Chicago Blackhawks. It forced them to trade away two rising stars (Boston shipping defenseman Dougie Hamilton to Calgary, Chicago dealing left wing Brandon Saad to Columbus), rather than risk losing them to other teams via expensive offer sheets.

Hamilton and Saad were tempting targets. Hamilton, 22, was seen as the heir apparent of aging Bruins captain Zdeno Chara, Saad, also 22, is a top-six winger who helped the Blackhawks win two Stanley Cups in three years.

Fear of an offer sheet forced the Bruins to trade Dougie Hamilton.

Fear of an offer sheet forced the Boston Bruins to trade Dougie Hamilton.

It wasn’t as though the Bruins and Blackhawks didn’t try to re-sign those players prior to July 1 (when they became restricted free agents), but their salary demands far exceeded what both clubs could afford within their respective salary-cap payrolls.  Hamilton and Saad sought over $6 million annually on long-term deals.

Both players were coming off entry-level contracts lacking arbitration rights. They used their respective teams’ limited cap space as leverage to secure more lucrative deals than they otherwise would’ve received if the Bruins and Blackhawks had more cap room. The threat of an offer sheet gave them leverage they otherwise wouldn’t have.

It’s a tactic rarely applied over the past decade. That’s because in every case but one (the Anaheim Ducks declining to match an offer sheet from the Edmonton Oilers for winger Dustin Penner in 2007) where a restricted free agent signed an offer sheet, it was matched by their current club.

It’s been speculated (but never proven) that NHL general managers were colluding to prevent offer sheets. This year, however, saw a set of circumstances create an atmosphere that made some GMs willing to test their luck.  The biggest factor was the marginal increase in the NHL’s salary-cap ceiling from $69 million to $71.4 million, providing teams carrying heavy payrolls (like Boston and Chicago) with only a limited increase in available space. A lack of top talent via this summer’s trade market and several teams changing management this year created a situation where offer sheets became a real threat.

In the past, teams with players coming off entry-level contracts had little reason to fear offer sheets. Their standard plan was to play hardball, using the player’s lack of negotiating leverage against them.  If a player didn’t receive an offer sheet, the only weapon at his disposal was to threaten a holdout, which in today’s salary-cap world has all the impact of a damp squib. Players who stage a holdout usually knuckle under after missing training camp or preseason.

Not this time. Not with the Bruins and Blackhawks facing a cap crunch and rival teams keen to test their willingness to match expensive offer sheets for Hamilton and Saad. The compensations (a first, second and third round pick in the 2016 NHL Draft) if they couldn’t match wasn’t worthwhile for either club. Rather than risk losing Hamilton and Saad, the Bruins and Blackhawks traded them for returns more palatable for their immediate plans.

This creates an interesting scenario going forward under the current NHL collective bargaining agreement. If league revenue continues to make only marginal gains in the foreseeable future, that means a slow annual rise in the salary cap. Seeing the Bruins and Blackhawks pressured by the threat of offer sheets to trade away two rising young stars could embolden other NHL general managers to try that tactic.

Next summer’s notable restricted free agents coming off entry-level deals includes Colorado Avalanche center Nathan MacKinnon, Nashville Predators winger Filip Forsberg and defenseman Seth Jones, plus St. Louis Blues winger Jaden Schwartz. Depending on their teams’ cap payroll and their respective performances next season, one or more of those rising young stars could become tempting offer-sheet targets.