mtg if you attacked can you block

[riolu]

if you attacked can you block?

[Arix]

That's what your creatures are there for. Once your opponent has finished declaring their attackers, you can choose to block with your own creatures, with a few stipulations.
1. Only untapped creatures can block.
2. One creature can't block multiple attackers (however, you can block one attacker with multiple creatures).
3. Take into account any evasion abilities that may affect blockers (for example, a creature without flying can't block a creature with flying).