OOTP includes an "acquired" field in the exported data, which is now summarized for each team and league on StatsPlus. Teams can acquire players in one of the following ways:
There are some rare cases where OOTP isn't able to classify the acquisition method, and these show as Unknown. For most leagues, these counts are very low and usually zero. One case OOTP doesn't seem to handle is Rule V draft returnees.
League > Reports > Roster Construction summarizes how all players on the current ML roster were acquired by their current team. This gives an easy way to compare different teams.
The default view shows a count of each type of acquisition, and using buttons at the top of the table can change the view to show WAR or current season salary by acquisition type.
Clicking on any entry in the table brings up a dialog listing all the players falling into the category, and shows more detail.


There's also a more detailed team breakdown available from a Team Page at Team Info > Acquired. This shows a graph of the acquisition type, and a table summarizing all the data.
