Quarters vs. HalvesThe NBA plays four 12-minute quarters. NCAA games are comprised of two 20-minute halves. In both the NBA and NCAA, an overtime period is five minutes.
The ClockThe NBA shot clock is 24 seconds. The NCAA shot clock is 35. This is one of several reasons you'll see such wide disparities in scoring in NCAA games - some teams really try to work the clock, play strong defense and end up with final scores in the 50-60 range. Others play up-tempo, hoist a lot of three-pointers, and post NBA-like scores in the 80s, 90s and 100s.
NCAA teams also have a little more time to advance the ball across half-court after a made basket: 10 seconds, as opposed to 8 in the NBA.
DistancesThe height of the basket and the distance between backboard and foul line is universal. The overall dimensions of the court - 94 feet long by 50 feet wide - are the same in NBA and NCAA ball as well. But that's where the similarities end.
The most obvious difference - one that you'll notice whenever a NCAA game is played in an NBA arena - is the shorter three-point shot at the collegiate level. An NBA "three" is taken from 23'9" (or 22" in the corners). The NCAA three-point line is a constant 19'9".
A subtler difference is the width of the lane, or the "paint." The NBA lane is 16 feet wide. In college it's 12 feet.
FoulsNBA players get six personal fouls before fouling out. NCAA players get five.
Then there's the tricky part: team fouls. First off, let's differentiate between shooting and non-shooting fouls. A player fouled in the act of shooting gets free throws, but other transgressions - "reaching in," for example - are "non-shooting" unless the offending team is "in the penalty." In other words, a team can commit a certain number of non-shooting fouls per period before giving up free throws to the other team.
With me so far? Good.
In the NBA, it's fairly simple. The fifth team foul per quarter puts a team in the penalty. After that, every foul - in the act of shooting or not - is worth two free throws.
In the NCAA, the penalty kicks in on the seventh team foul of the half. But that seventh foul gets a "one-and-one." The fouled player gets one free throw. If he makes it, he gets a second. With the tenth foul of the half, a team goes into the "double bonus" and all fouls are worth two free throws.
The bonus situation becomes crucial at the end of games. When trailing, teams will often foul to stop the clock. When in the one-and-one, that strategy is less risky - there's a chance that the opposing team will miss the first free throw attempt and give up a possession without increasing the lead. Once in the double-bonus, fouling to stop the clock is a riskier play.
PossessionIn the NBA, situations where possession of the ball is in dispute are resolved with a jump ball. In college, there's no jump ball after the opening tip. Possession simply alternates between teams. There's a "possession arrow" at the scorer's table that indicates which team will get the ball next.
DefenseThe rules governing defense in the NBA are impossibly complicated. Zone defenses - in which each player guards an area on the floor and not a specific man - are allowed, but only up to a point. The "Defensive Three Seconds" rule prohibits any defender from staying in the lane for more than three seconds unless he's directly guarding an offensive player; that basically prohibits the most essential form of zone defense, which is, "park your biggest guy right in the middle and tell him to swat any shot he can reach."
Some NBA teams play zone at times, but for the most part, the Association is a man-to-man league.
At the college level, there are no such rules. Over the course of a season, you'll see nearly as many defensive alignments as there are teams… from straight man-to-man to all sorts of zones to hybrids and "box-and-one" junk defenses to presses and traps.
For some college teams, a unique defense becomes a trademark of sorts. John Cheney, as coach at Temple, drove opponents nuts with an impenetrable matchup zone defense. Going a bit further back, Nolan Richardson, as coach of Arkansas, ran a frenetic full-court press he dubbed "40 Minutes of Hell." A clash of styles can make for really interesting matchups, especially at tournament time when teams face opponents that might be unfamiliar.