Stats fall into one of two categories: a rate state (e.g. ERA) or a counting stat (e.g. home runs). The conventional wisdom is that it is much harder to make up ground in rate stats than in counting stats. This is probably truer for pitching stats than hitting stats.
Counting stats are the product of rate stats and opportunities. Take the following arithmetic identity: Home runs equal home runs per plate appearance times the number of plate appearances.
HR = HR/PA * PA
So, there are two ways to up your home runs: have a player hit more home runs per plate appearance or have the player appear more often at the plate. For mixed leagues that aren’t extremely deep, most starting batters play full time, so there’s little margin to increase your players’ number of plate appearances. So catching up in offensive counting stats basically means finding players with better rates.
For pitching categories, life is a little different. You can stream two-start pitchers to increase your innings pitched, making advances in counting stats like strikeouts and wins (of course, likely at some cost to your rate stats). You can also shift to using more starters (or more relievers) to get more strikeouts (or saves).
Likewise, the category’s leader can make life tougher for you in some of the rate stats by switching to, for example, low-innings relief pitchers who will have less of an effect on ERA and WHIP. Again, this kind of strategy works better with pitchers than batters—relief pitchers can still help with saves, but there aren’t any (mainstream) counting stats that low-at-bat batters can help with. Moreover, there are generally more rate pitching stats than rate hitting stats. That said, this is an end-game strategy and not one that I’d recommend a category leader adopt more than a few weeks from the end of the season (if at all).
What does this mean for you now, midway through the season, if you’re trying to play catch-up in a rate or counting stat? At this point, I would think of rate stats and counting stats as the same and not be more despondent if I were lagging in one kind or the other. If you need to make up ground in a counting stat like strikeouts, look for pitchers with high K/9s and do not yet start streaming two-starters.
Moreover, with any kind of stat, look at the leaders. Have they gotten lucky? Ubaldo Jimenez’s owner is probably sitting pretty in your league, but even Jimenez’s ERA is likely to return somewhat to earth, and so will his owner’s.
Right now, rate stats and counting stats are the same still. Don’t give up on competing in a rate category just because it is a rate category. Just as important though, don’t forget that a counting category is still largely one of rates. If you want to hit .270 for the year and you’ve hit .260 for half a season, you’ll have to hit .280 for the second half. Ditto in counting stats: If you’re 10 home runs behind your targeted leader halfway through, you’ll have to hit at a rate that gives you 20 more home runs for the second half of the season in order to catch the leader (assuming his team stays at the same rate).