MLB Commissioner Rob Manfred explains the potential rule changes the league can use to increase the pace of the game. (1:58)

LAKELAND, Fla. -- Nothing about baseball "needs to be fixed," Rob Manfred said Thursday. But the commissioner then emphatically defended a series of pace-of-game proposals, saying his sport does need to change "so that baseball means as much to the next generation as it does to our generation."

Speaking at the annual Grapefruit League media day, Manfred spent most of a half-hour news conference pushing a series of potential changes that he hopes will create more action and less dead time.

MLB is currently negotiating with the players' association over which, if any, of the proposals will go into effect for this season.

Among the ideas Manfred endorsed were raising the strike zone, eliminating the intentional walk and finding ways to streamline instant replay.

On a proposal that would require managers to decide within 30 seconds whether to challenge a call, Manfred didn't specify an exact time but said, "I think field managers should have a time limit."

He also would like to see "reasonable limits" on how long umpires in the replay center should study replay angles before making a decision on whether to overturn a call. While he conceded that "we don't have that many 4-minute replays," he said: "But at some point, you've been looking at it for 3½ minutes, you sort of come to the conclusion that maybe it was close enough to right in the first instance, and we ought to move on with the game."

He admits that doing away with the intentional walk wouldn't save a lot of time, because intentional walks are at an all-time low point, "but it's dead time." And when it comes to every area of a game that carries built-in dead time, "there's probably not one" that he hasn't thought about ways to eliminate or limit, he said.

He said baseball has compiled data that shows that raising the bottom of the strike zone a couple of inches, to the top of the knee, would create more offense, more balls in play and more action. He said the strike zone has been creeping downward in recent years even though the rulebook definition of a strike hasn't changed. So raising the zone would actually just be a way of "restoring the natural order, and getting [the zone] back to where it was for a very long time," he said.

Asked if a few weeks of spring training would give players and umpires enough time to adjust to the new strike zone, the commissioner said: "I think spring training is sufficient in terms of the adjustment when you're talking about some of the best athletes in the world. ... And our umpires have shown an amazing ability, with proper feedback through technology, to call the strike zone as we ask them to call it." Sources have indicated, however, that the change in the strike zone is unlikely to be agreed to for this season.

Manfred also defended the experimentation, in the minor leagues, with starting extra innings with a runner on second base, even though it's a change "we don't expect to ever apply at the major league level." But he said, "We may learn something that would be helpful moving forward."

Finally, the commissioner said he knows that many fans resist changes in a game they love.

"Whenever you change something, there's a risk," Manfred said. "We know that, even from the little rule changes that we've made ...There's a period of adjustment. But you know what? We get through those periods of adjustment. Modern civilization does not come to an end. And the game is better at the end of it.

"I think we need to continue to be willing to look at the game, be thoughtful and reasonable and respectful of the history and traditions of the game, but also be willing to do things, with respect to rules, that will make the game better for our fans."