Methodology
Pace
As the name suggests, pace is an approximate measure of the speed of an NBA game. It is measured as the number of possessions per 48 minutes of game time which typically results in pace numbers in the 95-105 range.
There is an element of push and pull since in the same game, one team might milk the clock on every possession, while their opposition might run a seven-seconds-or-less style offense. In any given game, both teams end up with roughly the same number of possessions (within one), so the game's pace is a compromise between both teams' preferred tempos. Despite this, over the course of a season average pace will usually highlight teams which tend to play faster.
By the classic definition of pace, a single number is used for both teams. This makes sense when possession numbers are approximated from box score data and we don't know exactly how many possessions a team has had. However, when possession numbers are calculated from play-by-play data we can show pace on a per-team basis, though it's worth noting that the difference between the possessions counts of the two teams will only ever be a maximum of one possession.
Live pace
When a game is live we normalise pace values to a 48 minute game. This means we have a standard baseline for comparison between end-of-game pace and mid-game pace. To use a practical example let's say it is halftime and one team has used 50 possessions while their opponent has used 51. These numbers will be doubled in order to normalise them to 48 minutes. This results in a pace value of 101.
In the event that a game runs to one or more overtime periods, the pace numbers are normalised down to 48 minutes. The possession count may exceed the usual 95-105 range, but pace is still displayed relative to a 48 minute game. Again this helps make comparisons between games of different lengths more intuitive.
Pace and efficiency
Pace is what makes efficiency ratings meaningful. A team that scores 115 points sounds impressive, but if they used 110 possessions to get there, their offensive rating is only 104.5 points per 100 possessions, which is below the league average. Conversely, a team that scores 105 points on just 95 possessions has an offensive rating of 110.5, which is elite.
By expressing scoring as points per 100 possessions rather than raw points per game, efficiency ratings remove pace as a variable. This allows for fair comparisons between teams that play at different speeds, and between eras of basketball where the league-wide pace has varied significantly.
This is the crux of modern NBA analytics; pace-adjusted metrics. By removing pace as a variable, we can make meaningful comparisons between teams that play at different speeds. This tends to dispel historic biases which could tend to favour inefficient teams that play fast and score more points per game over slower but more efficient low-scoring teams. Raw points-per-game alone can be misleading.
Next up: Efficiency ratings