Pain and Injury
The receiver is at more risk for injury than the person penetrating them. It is true that if a man gets a little too enthusiastic and misses the anus, he can hit a hard part and fracture his penis. What's more common in anal, however, is the receiver experiences soreness or tearing that can result in bleeding. This is why it's important for partners to communicate. (Also, probably avoid numbing lubes). Because some level of anal tearing is common, it is also important to be safe during anal sex. Know your partner's status and make smart decisions about protection.