If an attacking creature with trample or trample over planeswalkers is blocked, but there are no creatures blocking it when damage is assigned, its damage is assigned to the defending player and/or planeswalker as though all blocking creatures have been assigned lethal damage.
May 3, 2019 · War of the Spark
If a creature with trample is attacking a planeswalker, none of its combat damage can be assigned to the defending player, even if that planeswalker has been removed from combat or the damage the attacking creature could assign is greater than the planeswalker’s loyalty.
January 25, 2019 · Ravnica Allegiance
If a creature with trample is attacking a planeswalker, none of its combat damage can be assigned to the defending player, even if that planeswalker has been removed from combat or the damage the attacking creature could assign is greater than the planeswalker's loyalty.
February 1, 2014 · Born of the Gods
If a creature with trample is attacking a planeswalker, none of its combat damage can be assigned to the defending player, even if that planeswalker has been removed from combat or the damage the attacking creature could assign is greater than the planeswalker’s loyalty.
July 13, 2013 · Magic 2014
If a creature with trample is attacking a planeswalker, none of its combat damage can be assigned to the defending player, even if that planeswalker has been removed from combat or the damage the attacking creature could assign is greater than the planeswalker's loyalty.
June 17, 2011 · Commander 2011
rule 702.19d not present in this release
February 1, 2010 · Worldwake
All creatures in an attacking band must attack the same player or planeswalker.