Most rivalries are forged from decades of tradition and animosity, but sometimes a single spark can ignite a powder keg and send two teams flying at each other's throat on every loose ball.
And in the postseason, there are sparks flying everywhere.
These are the instant playoff rivalries, the new seedlings in the history of the sport when two opponents continuously run afoul of one another in the postseason bracketing.
A few ingredients are necessary to form an instant rivalry: star power, parity, drama and aggression.
Fans want to see the stars butt heads. It recalls the glory days of playoff basketball, when Kevin McHale clotheslined Kurt Rambis or when Jeff Van Gundy clung to Alonzo Mourning's shin during a brawl.
Of course, no one wants to see a player (or coach) get hurt, but a little conflict adds plenty of spice to a matchup. And it's nice to see everyone playing with fire and full effort for a change.
In this year's postseason, some of the meetings are long-established rivalries, while others are merely lopsided blowouts and speed bumps before the conference semifinals. But some of them have evolved into knock-down, drag-out clashes worthy of a DVD box set.
Among the eight first-round matchups, four of them qualify as instant playoff rivalries. The only pity is that these epic clashes won't last more than seven games, because they are downright scintillating.