After several gruesome incidents in which fans were struck by balls and shattered bats at games last season, Major League Baseball on Wednesday issued a recommendation for all 30 clubs to erect protective netting in front of the most exposed field-level seats from one dugout to the other.

Some clubs, like the Boston Red Sox, who had two patrons hospitalized after being struck at Fenway Park, immediately promised to comply with the voluntary directive. Most, if not all, teams are expected to join in before opening day.

Other clubs, like the Mets, the Pittsburgh Pirates and the Minnesota Twins, already have netting down the first- and third-base lines. The Mets have had their netting up since Citi Field opened in 2009.

M.L.B. officials, sobered by the summer’s bloody incidents, have been studying the matter for several months and hired a consulting firm to work with teams and help them install the netting. The hope is to keep the netting as unobtrusive as possible while providing protection.