AD&D DM Guide is legendary in that you could read it today and still find something new that you missed the previous 99 times you read. I been running into this while particpating in Tim of Gothride Manor AD&D Campaign. I decided to collect these periodically into a series labeled Delving into AD&D.
Page 66 DMG
You can only charge once a turn
If you set a polearm with a point or a spear against a charging opponent and hit you do double damage.
More specifically once you charge you can't charge for 9 more rounds.