Reckless Stampede (Red)

Whenever a card defends this, clash with the defending hero. The winner deals 1 damage to the other hero. Each hero may put their revealed card on the bottom of its owner's deck.

Rulings

From the Super Slam release notes

Reckless Stampede’s ability triggers each time a defending card is added to its chain link. If multiple defending cards are declared at the same time against Reckless Stampede (e.g. during the defend step), each defending card being added will cause the ability to trigger. Each of those triggered effects will resolve independently of the other triggered effects.
When resolving Reckless Stampede’s triggered effect, there is no priority between any of the effects generated (e.g. clashing with the defending hero, dealing damage, each hero putting their revealed card).
When resolving Reckless Stampede’s triggered effect, if there are no defending heroes when this triggered effect resolves, the clash effect fails and there is no winner.
If multiple heroes are being attacked at the same time, then each defending card will cause the ability to trigger once with the clash against the hero that the card is defending.
If a card with protect is declared as a defending card for a Reckless Stampede that is targeting another player, then the clash will be with the hero being attacked (the defending hero) not with the player that owns/controls the card with protect.

Keyword notes

Clash - Clashing heroes reveal the top card of their deck. The hero that reveals the card with greatest {p} wins.

Clash is an effect keyword.
Effects that modify values of cards in your deck are considered when clashing (e.g. Kayo, Mutated Mass, etc.)
If you win a clash, the opponent is considered to have failed to win the clash.
If no one wins a clash, you’re both considered to have failed to win the clash.
If both you and the opponent reveal a card with the same , no one wins the clash.
If both you and the opponent reveal a card without and/or don’t reveal any card, no one wins the clash.
If you reveal a card with and the opponent reveals a card without , you win the clash.
If you reveal a card with and the opponent doesn’t reveal any card, you win the clash.