reason why you can play 'for free'

target of play 'for free'

Deep Space Station K-7
Station
Shields: 16
Plays at 2267 Sherman's Planet; may be used by all players' compatible cards. Once per turn, one card reporting at this location may report for free. (Not duplicatable.)

Agonizer, Classic Communicator, Classic Disruptor, Classic Medical Tricorder, Classic Tricorder, Classic Type II Phaser, Mirror Dagger, Romulan Cloaking Device, Arne Darvin, Balok, Captain Kirk, Captain Koloth, Chief Engineer Scott, Chief Navigator Chekov, Chief Surgeon McCoy, Commander Charvanek, Comm Officer Uhura, Crewman Wilson, Daval, Dr. McCoy (TwT), Dr. Roger Korby, D’vano, Ensign Chekov, Ensign Davis, Ensign Gaffney, Ensign O’Brien, First Officer Spock, Gem, Gorrus, James Tiberius Kirk, Keras, Kered, Korax, Kras, Lt. Bailey, Lt. Bashir, Lt. D’Amato, Lt. Dax, Lt. Grant, Lt. Kyle, Lt. Moreau, Lt. Nagata, Lt. Sisko, Lt. Sulu, Lt. Uhura, Lt. Watley, Marlena Moreau, Mr. Scott (TwT), Mr. Spock, Nilz Baris, Nurse Chapel, Odo (TwT), Ruk, Security Chief Sulu, Subcommander Tal, The Centurion, Transporter Chief Kyle, Worf, Wyatt Earp, Battle Cruiser, Columbus, Fesarius, Gal Gath’thong, I.K.C. Gr’oth, I.S.S. Constitution, I.S.S. Enterprise, Starship Constitution (MM), Starship Enterprise (MM)

Office of the President
Headquarters
Shields: 42
Seeds or plays on Earth. Once per turn, one Federation Ambrassador, Admiral, Vice-Admiral or President OR one HQ card may play for free there. (Not duplicatable.)

HQ: War Room, HQ: Ferengi Credit Exchange, HQ: Orbital Weapons Platform, HQ: Defensive Measures, HQ: Return Orb to Bajor, HQ: Secure Homeworld, Admiral Cartwright, Admiral Hayes, Admiral Janeway, Admiral J. P. Hanson, Admiral Kirk, Admiral Leyton, Admiral McCoy, Admiral Picard, Admiral Riker, Admiral Ross, Alynna Nechayev, Ambassador Krajensky, Ambassador Sarek, Andrea Brand, Academy Superintendent, Fleet Admiral Shanthi, Jaresh-Inyo, Kareel Odan, K’Ehleyr, Lojal, Matthew Dougherty, Neelix, Norah Satie, Sarek, Spock, St. John Talbot, T’Lara

Terran Rebellion HQ
Headquarters
Shields: 54
Seeds or plays on Terran Hideout; it is now the homeworld of cards. Once per turn, one personnel (except ) OR one HQ card may play for free here. (Not duplicatable.)

HQ: War Room, HQ: Ferengi Credit Exchange, HQ: Orbital Weapons Platform, HQ: Defensive Measures, HQ: Return Orb to Bajor, HQ: Secure Homeworld, Captain Bashir, Captain Dax, Commander Leeta, Ezri, Marauder, Mr. Andrews, Mr. Brunt, Mr. Nog, Mr. Quark, Mr. Rom, Mr. Sisko, Mr. Tuvok, Professor Sisko, Smiley