Out of the Park Baseball 9 added the ability to play with real Major League rosters for the first time in many years, (Previous versions prior to the first few versions required downloading fan made roster sets) although the re-released version of Out of the Park 8 had included this feature as well. It was also the first game in the series to feature in game sound effects during the play by play of games. Like all versions of the game, it also features many improvements to the AI of the computer controlled teams.
The game included a completely revised scouting system in which teams would hire a single scouting director, and then appropriate a scouting budget which could be delegated into a number of different areas, rather than the old system of micro-managing five different scouts in their day to day activities.
The financial system was tweaked from previous versions as well in order to be more transparent and allow players to see exactly where their teams budgets were going, as well as adding in several different customizable options for revenue sharing.
Additionally, the game revised the flexibility of the playoff format, allowing more customization of the playoffs than ever before. Beyond that, there were many fixes to how historical simulations play out, the way that personnel contracts are negotiated and a number of other improvements based on the previous version of the game.