Legal Question in Real Estate Law in Michigan

Only with permission, otherwise you are trespassing. That's the law because when someone is injured on another person's property, their entitlement to recovery of damages depends on their "status" at the time they were on the property, i.e., whether they were an invitee, trespasser, social guest, or licensee. Trespassers are afforded the least amount of recovery, for obvious reasons. Therefore, if you go onto the property to get the ball, and you trip and fall, or are bit by a dog, you may not be entitled to anything. It's always best to have permission to retrieve property that has accidentally traveled onto someone else's property - it's basic manners and decency, and also prevents legal battles or neighborly fights.

If someone's ball came into your yard, would you want them coming in your yard anytime they wanted? Probably not.