A possession is defined in tempo free usage as the time a team has the ball. The possession is ended by a made field goal or free throw, a defensive rebound (offensive boards extend the possession) or a turnover. Possessions can be calculated long hand while the convenient way, especially if you do not see the game or all of it, is by a formula.
POSS = (FGA + FTA * .475 + TO) - OREB
The .475 times FTA allows for free throws that are one shot on a potential three point play or a miss on the first attempt on a one and one. The formula often equals the amount of possessions recorded by long hand. If not, there is a slight difference.
The first half of Sunday’s St. John’s-Georgetown game I recorded possessions long hand on press row. I knew the total would be different. St. John’s attempted one free throw the first twenty minutes. AJ Storr, who hit the game winner from much farther distance, scored on a penetration move and was fouled. Storr missed the free throw. In calculating, the 1 free throw attempt times .475 = .475. Rounding up that .475 becomes a 1 (my concentration was high school guidance but I taught a few semesters of basic math). In long hand recording that free throw was part of one possession not a separate possession by itself.
For the half, the stat sheet on Mike Anderson’s group read like this.
Offensive efficiency (points per possession X 100) was 92.
My long hand calculations gave St. John’s 35 possessions. As noted the free throw attempt as part of an ‘and one’ already had a difference of one possession. The actual difference between formula and long hand was three possessions. A number of times I have recorded a half and found the formula and long hand equal. Three or four is about the highest difference total.
The formula, as noted, is very useful if you did not see the game or want a closer look at a particular outcome. Coaching staffs will utilize the formula while charting on the bench to see how a team reacted against a certain defense for example.
For the record, St. John’s scored on 15 of their 35 (43%) possessions that were charted. The Red Storm came up empty in the final seven possessions of the half. That was their longest drought the first twenty minutes. Not coincidentally, a time Georgetown made the run to take a four point lead into intermission. On the game, Kenpom.com calculated it a 71 possession pace (a uptempo number) with St. John's owning a 106-103 edge in offensive efficiency.