Admiral Adama from NuBSG. IIRC he was overall decent, but during the Pegasus episode he made an unbelievably reckless move that could have very nearly been the end for his faction.
Admiral Adama hears that Admiral Cain is going to execute his men. He phones up Cain and tells her that he's sending a shuttle over to retrieve his men from her ship. She can either have his men standing at the hangar ready for pick up, or a swat team can shoot their way through her ship and retrieve them. Cain launches her fighters to intercept the shuttle. Adama launches his fighters to counter hers.
Neither commander gives their fighters permission to shoot.
So what you have is both side's squadrons meet in the middle and begin circle strafing each other, nearly colliding with each other, each trying to get into the blind spot of each other. Whilst this is happening, the squadron leaders are begging their admirals to let them fire. The admirals were indecisive and squandered any advantages they might have had and recklessly endangered their men by putting them in such incredible danger. If they were going to send out the fighters in the first place, they should have committed and given them the authorization to shoot to defend themselves from the get go. If the admirals weren't willing to actually shoot the other side, then they shouldn't have sent out the fighters in the first place.
But this has broader implications than just the loss of the Galactica. The entire colonial fleet could have been lost. Adama did not tell the rest of the civilian fleet to jump away before he picked a fight with Cain. Adama knew that Cain had mugged civilian ships and left them to die. Cain does not recognize the authority of Adama or President Roslin. Adama has every reason to believe that the civilian ships are fair game to Cain. If the Pegasus did begin losing the battle, Cain could very well have begun shooting the civilian ships, thinking that she might be able to blackmail Galactica into standing down.
As aforementioned, there was great uncertainty over whether or not Galactica could defeat Pegasus. If Galactica was defeated, then the civilian fleet would have been at the mercy of the Pegasus, either being mugged, or enslaved, or blown up, or left to die. It would have been trivial for Adama - prior to phoning up Cain - to have told the civilian fleet to jump away to secret coordinates, and if a Galactica raptor didn't jump to those coordinates to give them the "okay" to regroup within a few days, then they should assume that Galactica lost and should continue their journey.
This is a pretty monumental screwup and could've cost Adama's side everything, all because he didn't send out a precautionary message.
Actually, challenging the Pegasus in the first place might have been Adama's biggest screwup. Yes, Adama loves his folk and isn't going to leave them to die, but he has greater responsibilities than to just two guys. He has a ship with thousands of crewmen on board, and has sworn to protect tens of thousands of civilians. Now, as a general rule of thumb, you shouldn't get into battles you don't have a high chance of winning. Up until now, Adama had little choice as to what battles he got into, with most of the time the Cylons were jumping on top of the fleet, but this time Adama actually has the choice whether or not to start this fight.
The odds are heavily stacked against Adama. Yes, Adama's men are more experienced, but the Galactica is objectively fighting a stronger ship, and Cain's crew feel like they are being driven into a corner. They're going to give everything they can. Even if Galactica was somehow able to defeat Pegasus, the losses on Adama's side would almost certainly be immense, and there is no guarantee that Galactica would even be able to fight again, let alone effectively. So there is an argument to be made that Adama might have just advised Roslin that Pegasus was more trouble than they were worth and for the entire fleet to jump away and leave Pegasus behind.
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Starfleet from DS9, after the Dominion War began. They had developed tons of very useful technology over the years that had been locked away. For example, the Genesis device. Phase-cloaking technology. Subspace weapons. Sniper rifles that could shoot through walls. Etc. Much of the time this tech was presumably locked away in a vault because Starfleet had moral qualms about using them, or were beholden to a treaty. From the TOS and Berman eras, you never really get the sense that the Federation-Romulan war or the Federation-Klingon war was an existential threat to the Federation, but a territorial war out on the frontier. But come DS9, the Federation is facing an existential threat. Starfleet should have begun using every advantage they had. Yeah, they might be breaking treaties, but if the Federation falls the Romulans and the Klingons likely will too. If the Federation survived the Romulans and the Klingons probably wouldn't press the issue, knowing that they had just been saved by the Federation, and the Federation just fought off the Dominion with these weapons so it'd probably be best not to antagonize them.