If a league has traditional playoffs, and the web tools are updated during a league's post-season or following off-season, a Playoff menu option will show on the primary League menu.

Note that the menu option does not show while the league is in pre-season, spring training, or the regular season, as no playoff information is available. To see past post-season results, use the Post-Season History feature.
If your league has a non-standard post-season and StatsPlus isn't able to show the status properly, the feature can be disabled on General Settings on the Admin Menu.

The top-level Playoff page will show data for each current or completed series in the post-season:

Clicking on the Series Detail link will show more information about the series, including the game-by-game results with links to the box scores on the OOTP HTML reports, and cumulative stats for each team in the series:
