VegasVideoHelp.com

Just as in most media player apps, hitting the spacebar in Vegas starts playback of your project. But, by default, hitting the spacebar again stops playback and sends the cursor back to where it started. If you’d rather that the cursor stay where it is so next time you can pick up where you left off, go to Options > Preferences. A bit over halfway down the list on the General tab is a checkbox to make the spacebar Play / Pause instead of Play / Stop.