The tacks deflated cyclists' tires, causing some competitors in the Patuxent Velo Cycling Club’s Leonardtown Criterium race to crash.
One cyclist broke a bone in a crash caused by a tack. Several others were injured.
Cyclist Bryan Vaughan got video of the crash in which he was involved. He said Keck Baker crashed and brought several other cyclists down with him.
Baker later pulled a tack out of his tire, according to Vaughan.
Cyclists can race at speeds exceeding 30 mph in such races, the sheriff's office said.
Anyone with information about the incidents should contact the sheriff's office at 301-475-4200, extension 1960, or Crime Solvers at 301-475-333. Tips also can be texted to "CRIMES" (274637). Type "TIP239" and your tip.