Local residents reported hearing an explosion, and no injuries or damage were reported. The IDF said the rocket did not cross into Israeli territory.
The siren, which sounded a little after 9pm, sent residents of the community into their protected areas. A short time later, Israeli Air Force planes struck a Hamas post in the northern Gaza Strip, the IDF said.
The siren created a great deal of panic at the event for children at a pool in the community.
"Eighty children were crammed into the protected area," local resident Yifat Ben Shoshan said. "There was a great panic."
She said the event was "the last night swim of the season" and was cut short.
"The children of Netiv Ha'Asara will remember this moment for the rest of their lives, that's for sure," she said.
The event comes amid heightened tensions in southern Israel.
On Tuesday, several mortar shells were fired at Israel, one of which exploded in an open area adjacent to the Gaza-Israel border.
There were no injuries or damage, and according to the IDF, additional mortar shells landed in the Gaza Strip.
As with multiple other attacks of this kind, the IDF response was measured, with aircraft striking Hamas positions in the northern Gaza Strip.
Two days ago, three rockets were launched at Sderot as thousands of people were enjoying a music festival in city.
Two of the rockets were intercepted by the Iron Dome missile defense system as concertgoers fled to reach protected areas.
The IDF attacked Hamas targets in the northern Gaza Strip in response. Among the targets was the office of a battalion commander in the terrorist organization.