The double lead-back of the same suit can be a powerful tool in a euchre game; however, for it to be effective it must be used correctly. The trick is to know how and when to use it. It is a common mistake to take a trick and lead the same suit back at the wrong time. Improperly use will, more often than not, result in your team being euchred.
Let's look at some of the times when the double lead will get your team in trouble. The worst offender is when your partner calls next and leads a small trump. You take that first trick then lead a trump back to your partner. This will most likely result in your team being euchred. Why? Many next calls are made on fairly weak hands, possibly holding only one or two trump. Leading trump a second time normally will pull out all the trump. Or even worst, may only leave trump in your opponent's hand. Once the trump is gone you are at the mercy of a strong green suit in the opposition's hand. The best thing to lead back is a green ace. If you don't have an Ace, lead back a card from your longest suit. This may allow your partner to trump in and it will make the best possible use of any trump held.
Going down the list, the next trouble spot for the double lead is when your team makes trump; your partner leads a small off-suit card. You take the trick and then lead the same suit back. Once a suit has been played, there will be very few left in that suit. There were only six cards to start with. (five if that suit is next) It's almost guaranteed to be trumped by someone. Leading back the same suit puts your partner in a precarious position. Being that the third seat sits behind your partner and has the last play, now your partner has to make a choice. Does he trump with a low card? If so, will it be overtrumped by the third seat? Does he trump using his highest trump? Should he hope the third seat is out of trump? At this point, there is no way for him to know for sure. He can only guess.
Another spot to watch is when you're in the first seat and your opponents make trump. If you take the first trick, a double lead gives the dealer the last play. Now your partner has to guess whether they should trump or let it go. If they trump is it over trumped? Did the bidder lead from a King - x set? Again, there is no way to know for sure.
So are there times when a double lead is a good thing? Yes. One of these times is when you sit in the seat just before the maker and you take a trick. Assuming they followed suit, this may be the best time to lead that same suit back. This play is called a 'lead through' and it works because, most likely, that will be the suit that they have two of. Remember, as the dealer, they already had the opportunity to discard and were able to create a void in their hand. There discard was likely a singleton suit and they still held a doubleton. Even if they didn't follow suit, they now have to choose between trumping or not. A double lead here should put your partner in a position to trump, or over-trump. There may even be times where they let the trick go by and your partner, in the third seat, will take it. Your partner may hold cards that could set up maker for an end play thus euchring them.
Because a double lead is the second lead, if you sit in the first seat and do trump, be sure to trump high. Remember, the bidder's partner sits behind you. In cases where the dealer's partner shows void in trump and this second lead is a boss card, you must trump in. Here it is acceptable to use a small trump.
A double lead can also be used to draw out a bidders trump. Why? The second lead is almost trumped by someone. It may be the bidder. While this would require a little planning, it could be used as a good method to set the maker up for a euchre. This works best if you hold power in trump.