The reasons why half the NBA can't trade their first-round pick right now

Rockets GM excited by flexibility of Harden deal (1:02)

Rockets general manager Rafael Stone describes the flexibility provided by the haul of first-round draft picks the Rockets acquired in exchange for James Harden. (1:02)

When Houston Rockets general manager Rafael Stone explained last week why he prioritized a bundle of first-round picks and not a current All-NBA player like Ben Simmons in a James Harden trade, he said it was because, "In the NBA, picks -- especially high picks -- are the best currency."

Those valuable picks, the lifeblood of so many blockbusters, are suddenly in very short supply.

Two developments over the past couple of years have frozen numerous teams out of trading picks for years on end. Currently, 15 teams are either out multiple first-round picks, forbidden from trading more, or have their picks locked -- "encumbered" in front-office vernacular, which means they can't trade them for multiple years.

The March 25 trade deadline was already set to challenge buyers as the new play-in tournament means 20 teams can make the "postseason" this year, incentivizing teams on the fringes from giving up. But coupled with the scarcity of picks available, the nature of trades could change for the foreseeable future.