The NL is averaging 3.89 runs per game with a .689 OPS. Their ISO is just .125. The AL is scoring 4.16 runs per game with a .712 OPS and a .139 ISO. Data from Baseball Reference. These numbers are even lower than they were in April and May. See my earlier post May Hitting About As Bad As April.
Last night there were 7 games with a total runs scored of 5 or less. That is between both teams. In 98 games so far in June, the NL has hit just 73 HRs. That would be about 120 per team for a whole season. The AL was a little better with 82 HRs in 88 games.
The table below shows the hitting stats in each month for both leagues in each of the last two years. The June numbers for 2010 are for the entire month.
The next table shows how each of those stats has changed.
Not sure if there is any kind of pattern other than that everything is down. It looks like the NL's power decline is even bigger than the AL's when you look at ISO.