Reckless Brute — ruling 1

Reckless Brute attacks only if it's able to do so as the declare attackers step begins. If, at that time, it's tapped, it's affected by a spell or ability that says it can't attack, then it doesn't attack. If there's a cost associated with having it attack, you're not forced to pay that cost, so it doesn't attack in that case either.

Reckless Brute — ruling 2

You choose which player or planeswalker Reckless Brute attacks.

Reckless Brute : règles, fonctionnement et interactions (MTG)

Reckless Brute is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Haste (This creature can attack and as soon as it comes under your control.) This creature attacks each combat if able.

How it works : Reckless Brute

Original English text — Wizards of the Coast / Scryfall

#1July 1, 2012· Wizards of the Coast
Reckless Brute attacks only if it's able to do so as the declare attackers step begins. If, at that time, it's tapped, it's affected by a spell or ability that says it can't attack, then it doesn't attack. If there's a cost associated with having it attack, you're not forced to pay that cost, so it doesn't attack in that case either.
No other card is named in this ruling.
#2July 1, 2012· Wizards of the Coast
You choose which player or planeswalker Reckless Brute attacks.
No other card is named in this ruling.