Reach does not restrict a creature to only blocking flying creatures — it simply adds the ability to block creatures with flying. Any creature without evasion can be blocked by any creature, reach or not, as long as no other restriction applies.
According to CR 702.17a, reach means the creature 'can block creatures with flying.' It grants an additional blocking permission beyond what a ground creature normally has. It does not change or limit what non-flying creatures the reach creature can block.
The flying ability (CR 702.9a) states that a creature with flying can only be blocked by creatures with flying or reach. Non-flying creatures have no such restriction on blockers — they can be blocked by every eligible creature, including those with reach.
Concrete example: You control a Spidery Grasp-enchanted creature (giving it reach). Your opponent attacks with both a 2/2 Bird (flying) and a 2/2 Bear (no flying). Your reach creature can legally block either one — the Bear because reach isn't required to block it, and the Bird because reach specifically grants that permission.
In short, reach is only relevant when you need to block a creature with flying. It provides no special benefit or restriction when blocking non-flying creatures.
Unofficial fan resource — not affiliated with or endorsed by Wizards of the Coast. Answers are AI-generated estimates grounded in the Comprehensive Rules and are not a substitute for an official judge. Verify anything match-critical.